Projection exposure apparatus

ABSTRACT

A projection exposure apparatus including an irradiation optical system including a light source and irradiating a mask with irradiation light beams, a projection optical system for projecting an image of a pattern of the mask on a substrate, a plurality of first fly-eye type optical integrators each having an emission side focal plane disposed on a Fourier transformed surface with respect to the pattern of the mask in the irradiation optical system or on a plane adjacent to the same and having a center located at a plurality of positions which are eccentric from the optical axis of the irradiation optical system, a plurality of second fly-eye type optical integrators each having an emission side focal plane disposed on a Fourier transformed plane with respect to the incidental end of each of a plurality of the first fly-eye type optical integrators or on a plane adjacent to the same and being disposed to correspond to a plurality of the first fly-eye type optical integrators, and a light divider for dividing and causing the irradiation light beams from the light source to be incident on each of a plurality of the second fly-eye type optical integrators.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a projection exposure apparatusfor use to form a pattern of a semiconductor integrated circuit, or aliquid crystal device, or the like.

[0003] 2. Related Background Art

[0004] When a circuit pattern of a semiconductor device or the like isformed, so-called photolithography technology is required. In thisprocess, a method, in which a reticle (a mask) pattern is formed on asubstrate such as semiconductor wafer, is usually employed. The surfaceof the substrate is applied with photosensitive photoresist so that acircuit pattern is transferred to the photoresist in accordance with animage irradiated with light, that is, in accordance with the shape ofthe pattern corresponding to a transparent portion of the reticlepattern. In a projection exposure apparatus (for example, a stepper),the image of a circuit pattern drawn on the reticle so as to betransferred is projected on the surface of the substrate (wafer) via aprojection optical system so as to be imaged.

[0005] In an irradiation optical system for irradiating the reticle withlight, an optical integrator such as a fly-eye type optical integrator(a fly-eye lens) and a fiber is used so as to uniform the distributionof the intensities of irradiation light with which the surface of thereticle is irradiated. In order to make the aforesaid intensitydistribution uniform optimally, a structure which employs the fly-eyelens is arranged in such a manner that the reticle-side focal surface(the emission side) and the surface of the reticle (the surface on whichthe pattern is formed) hold a substantially Fourier transformedrelationship. Also the focal surface adjacent to the reticle and thefocal surface adjacent to the light source (the incidental side) holdthe Fourier transformed relationship. Therefore, the surface of thereticle, on which the pattern is formed, and the focal surface of thefly-eye lens adjacent to the light source (correctly, the focal surfaceof each lens of the fly-eye lens adjacent to the light source) hold animage formative relationship (conjugated relationship). As a result ofthis, irradiation light beams from respective optical elements (asecondary light source image) of the fly-eye lens are added (superposed)because they pass through a condenser lens or the like so that they areaveraged on the reticle. Hence, the illuminance uniformity on thereticle can be improved. Incidentally, there has been disclosed anarrangement capable of improving the illuminance uniformity in U.S. Pat.No. 4,497,015 in which two pairs of optical integrators are disposed inseries.

[0006] In a conventional projection exposure apparatus, the lightquantity distribution of irradiation beams to be incident on the opticalintegrator, such as the aforesaid fly-eye lens, has been made to besubstantially uniform in a substantially circle area (or in arectangular area), the center of which is the optical system of theirradiation optical system.

[0007]FIG. 14 illustrates a schematic structure of a conventionalprojection exposure apparatus (stepper) of the above described type.Referring to FIG. 14, irradiation beams L140 pass through a fly-eye lens41 c, a spatial filter (an aperture diaphragm) 5 a and a condenser lens8 so that a pattern 10 of a reticle 9 is irradiated with the irradiationbeams L140. The spatial filter 5 a is disposed on, or adjacent to aFourier transformed surface 17 (hereinafter abbreviated to a “pupilsurface”) with respect to the reticle side focal surface 414 c of thefly-eye lens 41 c, that is, with respect to the reticle pattern 10.Furthermore, the spatial filter 5 a has a substantially circular openingcentered at a point on optical axis AX of a projection optical system 11so as to limit a secondary light source (plane light source) image to acircular shape. The irradiation light beams, which have passed throughthe pattern 10 of the reticle 9, are imaged on a resist layer of a wafer13 via the projection optical system 11. In the aforesaid structure, thenumber of apertures of the irradiation optical system (41 c, 5 a and 8)and the number of reticle-side apertures formed in the projectionoptical system 11, that is a value is determined by the aperturediaphragm (for example, by the diameter of an aperture formed in thespatial filter 5 a), the value being 0.3 to 0.6 in general.

[0008] The irradiation light beams L140 are diffracted by the pattern 10patterned by the reticle 9 so that 0-order diffracted light beam Do,+1-order diffracted light beam Dp and −1-order diffracted light beam Dmare generated from the pattern 10. The diffracted light beams Do, Dp andDm, thus generated, are condensed by the projection optical system 11 sothat interference fringes are generated. The interference fringes, thusgenerated, correspond to the image of the pattern 10. At this time,angle θ (reticle side) made by the 0-order diffracted light beam Do and±1-order diffracted light beams Dp and Dm is determined by an equationexpressed by sin θ=λ/P (λ: exposure wavelength and P: pattern pitch).

[0009] It should be noted that sin θ is enlarged in inverse proportionto the length of the pattern pitch, and therefore if sin θ has becomelarger than the number of apertures (NA_(R)) formed in the projectionoptical system 11 adjacent to the reticle 9, the ±1-order diffractedlight beams Dp and Dm are limited by he effective diameter of a pupil (aFourier transformed surface) 12 in the projection optical system 11. Asa result, the ±1-order diffracted light beams Dp and Dm cannot passthrough the projection optical system 11. At this time, only the 0-orderdiffracted light beam Do reaches the surface of the wafer 13 andtherefore no interference fringe is generated. That is, the image of thepattern 10 cannot be obtained in a case where sin θ>NA_(R). Hence, thepattern 10 cannot be transferred to the surface of the wafer 13.

[0010] It leads to a fact that pitch P, which holds the relationship sinθ=λ/P≡NA_(R), has been given by the following equation.

P≡λ/NA _(R)  (1)

[0011] Therefore, the minimum pattern size becomes about 0.5·λ/NA_(R)because the minimum pattern size is the half of the pitch P. However, inthe actual photolithography process, some considerable amount of focaldepth is required due to an influence of warp of the wafer, an influenceof stepped portions of the wafer generated during the process and thethickness of the photoresist. Hence, a practical minimum resolutionpattern size is expressed by k·λ/NA_(R), where k is a process factorwhich is about 0.6 to 0.8. Since the ratio of the reticle side number ofarticles NA_(W) and the wafer side number of articles NA_(R) is the sameas the imaging magnification of the projection optical system, theminimum resolution size on the reticle is k·λ/NA_(R) and the minimumpattern size on the wafer is k·λ/NA_(W)=k·λ/B·NA_(R) (where B is animaging magnification (contraction ratio)).

[0012] Therefore, a selection must be made whether an exposure lightsource having a shorter wavelength is used or a projection opticalsystem having a larger number of apertures is used in order to transfera more precise pattern. It might, of course, be considered feasible tostudy to optimize both the exposure wavelength and the number ofapertures.

[0013] However, it is so far difficult for the projection exposureapparatus of the above described type to shorten the wavelength of theirradiation light source (for example, 200 nm or shorter) because aproper optical material to make a transmissive optical member is notpresent and so forth. Furthermore, the number of apertures formed in theprojection optical system has approached its theoretical limit atpresent and therefore it is difficult to further enlarge the apertures.Even if the aperture can be further enlarged, the focal depth expressedby ±λ/2NA² rapidly decreases with an increase in the number ofapertures, causing a critical problem to take place in that the focaldepth required in a practical use further decreases.

[0014] In Japanese Patent Publication No. 62-50811 for example, therehas been disclosed a so-called phase shift reticle arranged in such amanner that the phase of each of transmissive light beams traveled fromspecific points in the transmissive portions of the circuit pattern ofthe reticle is shifted by π from the phase of transmissive light beamstraveled from the other transmissive portions. By using a phase shiftreticle of the type described above, a further precise pattern can betransferred.

[0015] However, the phase shift reticle has a multiplicity of unsolvedproblems because of a fact that the cost cannot be reduced due to itscomplicated manufacturing process and inspection and modificationmethods have not been established even now.

[0016] Hence, an attempt has been made as projection exposure technologywhich does not use the phase shift reticle and with which thetransference resolving power can be improved by modifying the method ofirradiating the reticle with light beams. One irradiation method of theaforesaid type is a so-called annular zone irradiation method, forexample, arranged in such a manner that the irradiation light beamswhich reach the reticle 9 are given a predetermined inclination bymaking the spatial filter 5 a shown in FIG. 14 an annular opening sothat the irradiation light beams distributed around the optical axis ofthe irradiation optical system are cut on the Fourier transformedsurface 17.

[0017] In order to establish projection exposure having a furtherimproved resolving power and a larger focal depth, an inclinationirradiation method or a deformed light source method has been previouslydisclosed in PCT/JP91/01103 (filed on Aug. 19, 1991). The aforesaidirradiation method is arranged in such a manner that a diaphragm (aspatial filter) having a plurality (two or four) openings, which aremade to be eccentric with respect to the optical axis of the irradiationoptical system by a quantity corresponding to the precision (the pitchor the like) of the reticle pattern, is disposed adjacent to theemission side focal surface of the fly-eye lens so that the reticlepattern is irradiated with the irradiation light beams from a specificdirection while inclining the light beams by a predetermined angle.

[0018] However, the above mentioned inclination irradiation method andthe deformed light source method have a problem in that it is difficultto realize a uniform illuminance distribution over the entire surface ofthe reticle because the number of effective lens elements (that is, thenumber of secondary light sources capable of passing through the spatialfilter) decreases and therefore an effect of making the illuminanceuniform on the reticle deteriorates. What is worse, the light quantityloss is excessive large in the system which has a member, such as thespatial filter, for partially cutting the irradiation light beams.Therefore, the illumination intensity (the illuminance) on the reticleor the wafer can, of course, deteriorate excessively, causing a problemto take place in that the time taken to complete the exposure processbecomes long with the deterioration in the irradiation efficiency.Furthermore, a fact that light beams emitted from the light sourceconcentrically pass through the Fourier transformed plane in theirradiation optical system will cause the temperature of a lightshielding member, such as the spatial filter, to rise excessively due toits light absorption and a measure (air cooling or the like) must betaken to prevent the performance deterioration due to change in theirradiation optical system caused from heat.

[0019] In a case where a diaphragm of the aforesaid type is disposedadjacent to the emission side focal surface of the fly-eye lens, some ofthe secondary light source images formed by a plurality of the lenselements are able to superpose on the boundary portion between the lighttransmissive portion of the diaphragm and the light shielding portion ofthe same. This means a fact that the secondary light source imageadjacent to the aforesaid boundary portion is shielded by the diaphragmor the same passes through the boundary portion on the contrary. Thatis, an unstable factor, such as the irradiation light quantity, isgenerated and another problem arises in that the light quantities of thelight beams emitted from the aforesaid diaphragm and that are incidenton the reticle become different from one another. Furthermore, in theinclination irradiation method, the positions of the four openings (inother words, the light quantity distribution in the Fourier transformedsurface) must be changed in accordance with the degree of precision ofthe reticle pattern (the line width, or the pitch or the like).Therefore, a plurality of diaphragms must be made to be exchangeable inthe irradiation optical system, causing a problem to arise in that thesize of the apparatus is enlarged.

[0020] When a secondary light source formed on the reticle side focalsurface of the fly-eye lens is considered in a case where the lightsource comprises a laser such as an excimer laser having a spatialcoherence, the irradiation light beams corresponding to the lenselements have some considerable amount of coherence from each other. Asa result, random interference fringes (speckle interference fringes) areformed on the surface of the reticle or the surface of the wafer whichis in conjugate with the surface of the reticle, causing the illuminanceuniformity to deteriorate. When its spatial frequency is consideredhere, a Fourier component corresponding to the minimum interval betweenthe lens elements is present in main. That is, the number ofcombinations of light beams contributing to the interference is thelargest. Therefore, fringes having a relatively low frequency (having along pitch) in comparison to the limit resolution and formed tocorrespond to the configuration direction of the lens elements areobserved on the surface of the reticle or the surface of the wafer.Although the formed interference fringes have low contrast because theKrF excimer laser has a relatively low spatial coherence, theinterference fringe acts as parasite noise for the original pattern. Thegeneration of the interference fringes causes a problem when theilluminance uniformity, which will be further required in the future, isimproved. In the case where the annular zone irradiation method isconsidered, the aforesaid noise concentrically superposes in thevicinity of the limit resolution, and therefore the influence of thenoise is relatively critical in comparison to the ordinary irradiationmethod (see FIG. 14).

SUMMARY OF THE INVENTION

[0021] An object of the present invention is to provide a projectionexposure apparatus capable of obtaining high resolution and a largefocal depth and revealing excellent illuminance uniformity even if anordinary reticle is used.

[0022] In the present invention, the emission side focal surface isdisposed on a Fourier transformed surface 17 with respect to a mask inthe optical path of the irradiation optical system or on a planeadjacent to the same as shown in FIG. 1. Furthermore, there are aplurality of first fly-eye lenses 41 a and 41 b the centers of which aredisposed at a plurality of positions which are eccentric from opticalaxis AX of the irradiation optical system, a plurality of second fly-eyelenses 40 a and 40 b having the emission side focal plane located on theFourier transformed surface with respect to each incidental end of aplurality of the first fly-eye lenses 41 a and 41 b or on a surfaceadjacent to the same and disposed to correspond to the first fly-eyelenses 41 a and 41 b and light dividers for dividing the irradiationlight beams from the light source to be incident on a plurality of thesecond fly-eye lenses 40 a and 40 b. Furthermore, a guide opticalelement is disposed so as to cause the light beams emitted from one of aplurality of the second fly-eye lenses to be incident on one of aplurality of the first fly-eye lenses. In a case where a laserrepresented by an exccimerlaser is used as the light source, an opticalpath difference generating member 70 is disposed between a plurality ofthe light beams emitted from the light dividers 20 and 21 shown in FIG.17, the optical path difference generating member 70 causing an opticalpath difference (the phase difference) longer than the coherent distance(the coherent length) of the irradiation light beams to be given.

[0023] As shown in FIGS. 24 and 27, the present invention comprises, inan irradiation optical path, a plane light source forming optical system100 or 106 and 107 for forming a plurality of light sources, aconverging optical system 102 or 108 for converging the light beams fromthe plane light source forming optical system, a polyhedron light sourceforming optical system 103 having a plurality of lens elements 103 a to103 d for forming a plurality of plane light source images on theFourier transformed surface with respect to the reticle by the lightbeams from the converging optical system or on a plane adjacent to thesame and having the centers of the optical axes disposed at a pluralityof positions which are eccentric from the optical axis of theirradiation optical system, and a condenser for converging the lightbeams from the plurality of plane light source images formed by thepolyhedro light source forming optical system onto the reticle.

[0024] In the aforesaid basic structure, assuming that half of thedistance between the optical axes of the lens elements in a direction ofthe pattern of said reticle is L, the focal distance on the emissionside of said condenser lens is f, the wavelength of said irradiationlight beams is λ and the cyclic pitch of said pattern of said mask is P,it is preferable to arrange the structure to satisfy the followingcondition:

L=λf/2P

[0025] In a case where the reticle has a two-dimensional pattern, thepolyhedron light source forming optical system is composed of four lenselements disposed in parallel and, assuming that the number of apertureson the reticle side of said projection optical system is NA_(R), half ofthe distance between the optical axes of said lens elements 103 a to 103d in a direction of the pattern of the reticle is L, and the emissionside focal distance of the condenser lens 8 is f, it is preferable thatthe following conditions are satisfied:

0.35 NA _(R) ≦L/f≦0.7 NA _(R)

[0026] As shown in FIG. 29, the present invention comprises lightdividers 200 and 201 for dividing the irradiation light beams in theoptical path of the irradiation optical system, polyhedron light sourceforming optical systems 202 a, 202 b, 203 a, 203 b, 204 a and 204 b forforming a plurality of plane light sources which correspond to eachlight beam divided by the light dividers on the Fourier transformedsurface with respect to the reticle 9 or on a plane adjacent to the sameat a plurality of positions which are eccentric from the optical axis ofthe irradiation optical system and a condenser lens 8 for converging thelight beams from a plurality of the plane light sources onto thereticle, wherein the polyhedron light source forming optical systemincludes at least rod type optical integrators 203 a and 203 b.

[0027] In the aforesaid basic structure, the polyhedron light sourceforming optical system may have a plurality of rod type opticalintegrators the centers of which are disposed at a plurality ofpositions which are eccentric from the optical axis of the irradiationoptical system.

[0028] Furthermore, the polyhedron light source forming optical systemmay comprise a first converging lens for converging light beams dividedby the light dividing optical system, a rod type optical integratorhaving the incidental surface disposed at the focal point of theconverging lens and a second converging lens for converging the lightbeams from the rod type optical integrator to form a plurality of planelight sources on the Fourier transformed surface with respect to thereticle or on a plane adjacent to the same.

[0029] The operation of the present invention will now be described withreference to FIG. 13. The description will be given hereinafter about anexample of the projection exposure apparatus in which the fly-eye typeoptical integrator (fly-eye lens) is disposed in the irradiation opticalsystem. Referring to FIG. 13, second fly-eye lens groups 40 a and 40 bcorresponding to the second fly-eye lens according to the presentinvention are disposed on a plane perpendicular to optical axis AX.Light beams emitted from them are incident on first fly-eye lens groups41 a and 42 b, which correspond to the first fly-eye lens according tothe present invention, by guide optical systems 42 a and 42 b. Theilluminance distribution on the incidental surface of the first fly-eyelens is made uniform by the second fly-eye lens group.

[0030] Light beams emitted from the first fly-eye lens group are appliedto a reticle 9 by a condenser lens 8. The illuminance distribution onthe reticle 9 is made to be uniform by the first and the second fly-eyelens groups to a satisfactory degree. Reticle side focal surfaces 414 aand 414 b of the first fly-eye lens groups 41 a and 41 b substantiallycoincide with a Fourier transformed surface 17 of the reticle pattern10. Therefore, the distance from optical axis AX to the center of thefirst fly-eye lens corresponds to the incidental angle of the lightbeams emitted from the first fly-eye lens on the reticle 9.

[0031] A circuit pattern 10 drawn on the reticle (the mask) includes amultiplicity of cyclic patterns. Therefore, the reticle pattern 10irradiated with the irradiation light beams emitted from one fly-eyelens group 41 a generates a 0-order diffracted light beam component Do,±1-order diffracted light beam components Dp and Dm and higherdiffracted light beam components in a direction corresponding to theprecision of the pattern.

[0032] At this time, since the irradiation light beams (the main beams)are incident on the reticle while being inclined, also the diffractedlight beam components are generated from the reticle pattern 10 whilebeing inclined (having an angular deviation) in comparison to a casewhere the reticle 9 is irradiated perpendicularly. Irradiation lightbeam L130 shown in FIG. 13 is incident on the reticle 9 while beinginclined by φ from the optical axis.

[0033] Irradiation light beam L130 is diffracted by the reticle pattern10 and the 0-order diffracted light beam Do travelling in a directioninclined by φ from optical axis AX, +1-order diffracted light beam Dpinclined from the 0-order diffracted light beam by θp and the −1-orderdiffracted light beam Dm travelling while being inclined from the0-order diffracted light beam Do by θm are generated. However, sinceirradiation light beam L130 is incident on the reticle pattern whilebeing inclined from optical axis AX of the double telecentric projectionoptical system 11 by an angle φ, also the 0-order diffracted light beamDo also travels in a direction inclined by an angle Φ from optical axisof the projection optical system.

[0034] Therefore, the +1-order diffracted light beam Dp travels in adirection θp+Φ with respect to optical axis AX, while the −1-orderdiffracted light beam Dm travels in a direction θm-φ with respect tooptical axis AX.

[0035] At this time, the diffracted angles θp and θm respectively areexpressed by:

sin (θp+φ)−sinφ=λ/P  (2)

sin (θm−φ)+sinφ=λ/P  (3)

[0036] Assumption is made here that both of the +1-order diffractedlight beam Dp and the −1-order diffracted light beam Dm pass through apupil surface 12 of the projection optical system 11.

[0037] When the diffraction angle is enlarged with the precision of thereticle pattern 10, the +1-order diffracted light beam Dp travelling inthe direction θp +φ cannot pass through the pupil 12 of the projectionoptical system 11. That is, a relationship expressed by sin (θp+φ)>NA_(R) is realized. However, since irradiation light beam L130 isincident while being inclined from optical axis AX, the −1-orderdiffracted light beam Dm is able to pass through the projection opticalsystem 11 at the aforesaid diffraction angle. That is, a relationshipexpressed by sin (θm−φ)<NA_(R) is realized.

[0038] Therefore, interference fringes are generated on the wafer due tothe 0-order diffracted light beam Do and the −1-order diffracted lightbeam Dm. The aforesaid interference fringes are the image of the reticlepattern 10. When the reticle pattern is formed into a line-and-spacepattern having a ratio of 1:1, the image of the reticle pattern 10 canbe patterned on the resist applied on the wafer 13 while having acontrast of about 90%.

[0039] At this time, the resolution limit is present when the followingrelationship is realized:

sin (θm−φ)=NA _(R)  (4)

[0040] Therefore, the pitch on the reticle side of the minimum patternwhich can be allowed to be transferred can be expressed by:

NA _(R)+sin φ=λ/P

P≡λ/(NA _(R)+sin φ)  (5)

[0041] In a case where sin φ is made to be about 0.5×NA_(R), the minimumpitch of the pattern on the reticle which can be transferred becomes asfollows:

P=λ/(NA _(R)+0.5 NA _(R))

=2λ/3NA _(R)  (6)

[0042] In a case of a conventional exposure apparatus shown in FIG. 14in which the irradiation light beam distribution on the pupil 17 is in acircular region relative to optical axis AX of the projection opticalsystem 11, the resolution light is P=λ/NA_(R) as expressed by Equation(1). Therefore, the present invention enables a higher resolution incomparison to the conventional exposure apparatus.

[0043] Now, the description will be given about the reason why the focaldepth can be enlarged by irradiating the reticle pattern with exposurelight beams from a specific incidental direction and at a specific angleby a method in which the image pattern is formed on the wafer by usingthe 0-order diffracted light beam component and the 1-order diffractedlight beam component.

[0044] In a case where the wafer 13 coincides with the focal pointposition (the best imaging surface) of the projection optical system 11,the diffracted light beams emitted from a point of the reticle pattern10 and reaching a point on the wafer have the same optical path lengthregardless of the portion of the projection optical system 11 throughwhich they pass. Therefore, even in the conventional case where the0-order diffracted light beam component passes through substantially thecenter (adjacent to the optical axis) of the pupil surface 12 of theprojection optical system 11, optical length for the 0-order diffractedlight beam component and that for the other diffracted light beamcomponent are substantially the same and the mutual wavelengthaberration is zero. However, in a defocus state in which the wafer 13does not coincide with the focal point position of the projectionoptical system 11, the optical path length for a higher diffracted lightbeam made incident diagonally becomes short in front of the focal pointin comparison to the 0-order diffracted light beam which passes througha portion adjacent to the optical axis and as well as lengthened in therear of the focal point (toward the projection optical system 11) by adegree corresponding to the difference in the incidental angle.Therefore, the diffracted light beams such as 0-order, 1-order andhigher order diffracted light beams form mutual wave aberration, causingan out of focus image to be generated in front or in the rear of thefocal point position.

[0045] The wave aberration generated due to the defocus is a quantitygiven by ΔFr2/2 assuming that the quantity of deviation from the focalpoint position of the wafer 13 is ΔF and the sine of incidental angle θwmade when each diffracted light beam is incident on one point of thewafer is r (r=sin θw), where r is the distance between each diffractedlight beam and optical axis AX on the pupil surface 12. In theconventional projection exposure apparatus shown in FIG. 14, the 0-orderdiffracted light beam Do passes through a position adjacent to theoptical axis. Therefore, r (0-order) becomes 0, while 35 1-orderdiffracted light beams Dp and Dm hold a relationship expressed by r(1-order)=M·λ/P (where M is the magnification of the projection opticalsystem). Therefore, the wave aberration between the 0-order diffractedlight beam Do and ±1-order diffracted light beams Dp and Dm becomes:

ΔF·M2 (λ/P)2/2

[0046] In the projection exposure apparatus according to the presentinvention, the 0-order diffracted light component Do is generated in adirection inclined from optical axis AX by an angle φ as shown in FIG.13. Therefore, the distance between the 0-order diffracted light beamcomponent and the optical axis AX on the pupil surface 12 holds arelationship expressed by r (0-order)=M·sin φ.

[0047] The distance between the −1-order diffracted light beam componentand the optical axis on the pupil surface becomes a value obtainablefrom r (−1-order)=M·sin (θm−φ). If sin φ=sin (θm−φ) at this time, therelative wave aberration between the 0-order diffracted light beamcomponent Do and the −1-order diffracted light beam component Dm due tdefocus becomes zero. Hence, even if the wafer 13 is slightly deviatedin the direction of the optical axis from the focal point position, theout of focus of the image of the pattern 10 can be prevented. That is,the focal depth can be enlarged. Furthermore, since sin (θm−φ)+sin φ=λ/Pas expressed by the equation (3), the focal depth can be significantlyenlarged by causing the incident angle φ for the irradiation light beamL130 on the reticle 9 to hold a relationship expressed by sin φ=λ/2Pwith the pattern having pitch P.

[0048] In the present invention, the irradiation light beams emittedfrom the light source are divided into a plurality of light beams beforethey are introduced into each fly-eye lens. Therefore, the light beamsemitted from the light source can be efficiently utilized while reducingloss, so that a projection exposure system revealing high resolution anda large focal depth can be realized.

[0049] As described above, according to the present invention, thenecessity lies in simple fact that the irradiation optical system of theprojection exposure apparatus which is being operated is changed at themanufacturing process. Therefore, the projection optical system of anapparatus which is being operated can be utilized as it is and furtherimproved resolution and dense integration can be realized.

[0050] Although the irradiation system for use in the present inventionbecomes complicated in comparison to an ordinary system, the uniformityof the illuminance on the reticle surface and on the wafer surface canbe improved because the fly-eye lenses are disposed to form two stagesin the direction of the optical axis. By virtue of the two stage fly-eyelens structure, the illuminance uniformity on the reticle and the wafersurfaces can be maintained even if the fly-eye lens is moved on a planeperpendicular to the optical axis.

[0051] Since the light dividing optical system efficiently introducesthe irradiation light beams to the first stage fly-eye lens, theirradiation light quantity loss can be satisfactorily prevented.Therefore, the exposure time can be shortened and the processingperformance (throughput) cannot deteriorate.

[0052] In a system in which the second stage fly-eye lens adjacent tothe reticle is made movable as in an embodiment (see FIG. 5), optimumirradiation can be performed in accordance with the reticle pattern.

[0053] In a system arranged in such a manner that the first, the secondfly-eye lenses and the guide optical system are integrally held whilemaking them to be movable, the movable portion can be decreased andtherefore the structure can be simplified. As a result, themanufacturing and adjustment cost can be reduced.

[0054] Also in a case where a plurality of the guide optical system andthe corresponding first fly-eye lens are respectively made movable, thelight dividing optical system and the second fly-eye lens group areintegrally held. Therefore, the structure can be simplified and as wellas the manufacturing cost and the adjustment cost can be reduced.

[0055] In a system in which the light dividing optical system or aportion of the same is made to be movable, the optimum dividing opticalsystem (dividing into two portions and that into four portions can beselected) can be used in accordance with the division conditions.

[0056] In a system in which at least a portion of the light dividingoptical system can be moved or rotated, the condition of dividing thelight beams can be varied by, for example, changing the interval betweenthe polyhedron prisms or by rotating the polyhedron prism. Therefore, avariety of division states can be created by using a small number ofoptical members.

[0057] Also in a case where a rod type optical integrator is used inplace of the fly-eye type optical integrator (the fly-eye lens), or in acase where they are combined to each other, an effect similar to theaforesaid structures can be obtained.

[0058] Furthermore, the present invention is arranged in such a mannerthat the irradiation light beams emitted from the light source aredivided into a plurality of light beams before a phase difference (thedifference in the length of the optical path) which is longer than thecoherent distance (coherent length) of the irradiation light beams isgiven to a portion between a plurality of the light beams. The coherentlength LS of the irradiation light beam can be expressed by:

LS=λ2/Dl

[0059] (where the wave length of the irradiation light beam is λ and itsvector width is Dl).

[0060] That is, if a difference in the optical path length longer thanthe coherent length L is present between two light beams emitted fromone light source, the two light beams do not interfere with each other.In a case where the light source is a narrow band KrF excimer laser, thecoherent length L is about 20 mm and therefore an optical pathdifference can be relatively easily given to a plurality of light beams.Therefore, even if a laser having a certain coherence is used, thespeckle interference fringe which can be superposed on the desiredpattern as noise can be effectively reduced. That is, the illuminanceuniformity on the reticle and the wafer can be improved by necessitatinga simple structure in which the optical path difference generatingmember is disposed in the irradiation optical path.

[0061] Other and further objects, features and advantages of theinvention will be appeared more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0062]FIG. 1 is a view which illustrates the structure of a firstembodiment of a projection exposure apparatus according to the presentinvention;

[0063]FIG. 2 is a view which illustrates a portion of the structure ofthe irradiation optical system shown in FIG. 1;

[0064]FIGS. 3A and 3B are views which illustrate the structure of aprism for dividing the light divider in the irradiation optical systeminto four portions;

[0065]FIG. 4 is a view which illustrates the structure of a movingmechanism for fly-eye lens groups;

[0066]FIG. 5 is a view which illustrates a modification of a partialstructure of the irradiation optical system;

[0067]FIG. 6 is a view which illustrates a first modification of thelight divider in the irradiation optical system;

[0068]FIG. 7 is a view which illustrates a second modification of thelight divider in the irradiation optical system;

[0069]FIG. 8 is a view which illustrates a third modification of thelight divider in the irradiation optical system;

[0070]FIG. 9 is a view which illustrates another structure of theirradiation optical system;

[0071]FIGS. 10A to 10D are views which illustrate some structures of theelements of the fly-eye lens;

[0072]FIG. 11 is a view which illustrates the principle of theconfiguration of the fly-eye lenses in the irradiation optical system;

[0073]FIGS. 12A to 12D are views which illustrate a method of disposingthe fly-eye lenses;

[0074]FIG. 13 is a view which illustrates the structure of the apparatusfor describing the principle of the present invention;

[0075]FIG. 14 is a view which illustrates the principle of projectionperformed by a conventional projection exposure apparatus;

[0076]FIG. 15 is a view which illustrates the structure of a prism fordividing the irradiation light beams into four portions in theirradiation optical system;

[0077]FIG. 16 is a view which illustrates the schematic structure of theirradiation optical system having the prism shown in FIG. 15;

[0078]FIG. 17 is a view which illustrates the schematic structure of asecond embodiment of the projection exposure apparatus according to thepresent invention;

[0079]FIG. 18 is a view which illustrates the schematic structure of aportion of the irradiation optical system shown in FIG. 17;

[0080]FIG. 19 is a view which illustrates a modification of the partialstructure of the irradiation optical system shown in FIG. 17;

[0081]FIG. 20 is a view which illustrates a modification of the partialstructure of the irradiation optical system shown in FIG. 17;

[0082]FIG. 21 is a view which illustrates a modification of the partialstructure of the irradiation optical system shown in FIG. 17;

[0083]FIGS. 22A and 22B are views which illustrate a modification of theoptical path difference generating member in the irradiation opticalsystem;

[0084]FIGS. 23A and 23B are views which illustrate an example in whichan optical difference generating member is applied to the projectionexposure apparatus adapted to an annular zone irradiation method;

[0085]FIG. 24 is a view which illustrates the structure of a thirdembodiment of the projection exposure apparatus according to the presentinvention;

[0086]FIG. 25 illustrates a state of a light source image formed on theinjection surface of a polyhedron light source forming optical system;

[0087]FIG. 26 illustrates the principle of configuration of thepolyhedron light source forming optical system;

[0088]FIG. 27 is a view which illustrates the structure of a fourthembodiment of the projection exposure apparatus according to the presentinvention;

[0089]FIGS. 28A and 28B illustrate an example in which an afocalmagnification-varying optical system is disposed between the input lensand the fly-eye lens in the irradiation optical system;

[0090]FIG. 29 is a view which illustrates the structure of a fifthembodiment of the projection exposure apparatus according to the presentinvention;

[0091]FIGS. 30A and 30B are views which illustrate an example of thelight divider shown in FIG. 29;

[0092]FIG. 31 is a view which illustrates a portion of the irradiationoptical system shown in FIG. 29;

[0093]FIG. 32 is a view which illustrates the structure of a sixthembodiment of the projection exposure apparatus according to the presentinvention; and

[0094]FIG. 33 is a view which illustrates the structure of a seventhembodiment of the projection exposure apparatus according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0095]FIG. 1 illustrates a first embodiment of the present invention inwhich two polyhedron prisms are used to form a light dividing opticalsystem.

[0096] Irradiation light beams emitted from a light source 1 such as amercury lamp are gathered by an elliptical mirror 2 before they are madeto be substantially parallel beams by a bending mirror 3 and an inputlens 4 so that the light beams are incident on light dividing opticalsystems 20 and 21. A light divider according to this embodimentcomprises a first polyhedron prism 20 having a V-shape concave and apolyhedron prism 21 having a V-shape convex. The irradiation light beamsare divided into two light beams by the refraction effect of theaforesaid two prisms 20 and 21. The divided light beams are respectivelyincident on second fly-eye lenses 40 a and 40 b.

[0097] Although two fly-eye lenses 40 a and 40 b are used in thisembodiment, the quantity of them may be determined arbitrarily. Althoughthe light dividing optical system is arranged to divide the light beamsinto two sections to correspond to the number of the second fly-eye lensgroups, the light beams may be divided into an arbitrary number ofsections to correspond to the number of the second fly-eye lens groups.For example, in an arrangement in which the second fly-eye lens group iscomposed of four lenses, each of the light dividing optical systems 20and 21 may be composed of a first polyhedron prism 20 having a pyramidconcave and a second polyhedron prism 21 having a pyramid convex. Theirradiation light beams emitted from the second fly-eye lens groups 40 aand 40 b are respectively incident on first fly-eye lens groups 41 a and41 b by guide optical systems 42 a, 43 a, 42 b and 43 b. At this time,the first fly-eye lens 41 a receives only the light beam travelled fromthe second fly-eye lens 40 a, while the first fly-eye lens 41 b receivesonly the light beam travelled from the second fly-eye lens 40 b.

[0098] The light beams emitted from the first fly-eye lenses 41 a and 41b are introduced by condenser lenses 6 and 8 and a bending mirror 7 soas to irradiate a pattern 10 formed on the lower surface of a reticle 9.The light beams, which have passed through the pattern 10, are gatheredand imaged by a projection optical system 11 so that the image of thepattern 10 is formed on a wafer 13.

[0099] It should be noted that reference numeral 12 represents a Fouriertransformed surface (hereinafter called a “pupil surface or plane of theprojection optical system”) in the projection optical system 11 withrespect to the pattern 10, the arrangement being sometimes arranged insuch a manner that the pupil surface of the projection optical system isprovided with a variable diaphragm (NA diaphragm).

[0100] Also the irradiation optical system includes a pupil surface 17of the irradiation optical system corresponding to the Fouriertransformed surface with respect to the pattern 10. The reticle sidefocal surface (emission side focal surface) of each of the aforesaidfirst fly-eye lenses 41 a and 41 b is present at a position whichsubstantially coincides with the pupil surface 17 of the irradiationoptical system. The emission sides of the second fly-eye lenses 40 a and40 b are Fourier transformed surfaces with respect to the incidentalsurfaces of the first fly-eye lenses 41 a and 41 b by guide opticalsystems 42 and 43. However, the necessity of strictly maintaining theFourier transformed relationship can be eliminated if a relationship canbe maintained in which the light beams emitted from the respectiveelements of the second fly-eye lens in each pair of the fly-eye lenses40 a, 41 a, and the fly-eye lenses 40 b,41 b are superposed on oneanother on the incidental surface of the first fly-eye lens.

[0101] The structure of each fly-eye lens will now be described withreference to FIG. 10. FIGS. 10A to 10D are enlarged views whichillustrate an element of the fly-eye lens. Actual fly-eye lenses, forexample, fly-eye lenses 40 a, 40 b, 41 a and 41 b shown in FIG. 1 areaggregates of the aforesaid elements. Some of the elements are arranged(aggregated) in a direction from the upper portion to the lower portionof FIG. 10 and a vertical direction to the surface of the drawing sheetto form one element.

[0102]FIG. 10A illustrates a state where an incidental surface 401 a andthe light source side focal surface 403 a coincide with each other andan emission surface 402 a and a reticle side focal surface 404 bcoincide with each other. In the embodiment shown in FIG. 1 and in otherembodiments, the fly-eye lens of the type shown in FIG. 10A is usedunless otherwise specified.

[0103] Parallel light beams 410 a which have been incident from a lightsource (in the left portion of the drawing) are gathered to a reticleside focal plane 404 a as designated by a solid line, while light beams(designated by a dashed line) emitted from one point on the light sourceside focal surface 403 a are made to be parallel light beams after theyhave been emitted. Types respectively shown in FIGS. 10B to 10D will bedescribed later.

[0104] The light side focal surfaces (which coincide with the incidentalsurfaces here) of the second fly-eye lens groups 40 a and 40 b and thefirst fly-eye lens group 41 a and 41 b shown in FIG. 1 hold the imageforming relationship as described above. Therefore, the light beams,which have been incident on the incidental surface of each element of,for example, 40 a included by the second fly-eye lens group are imagedand projected on all of the elements of the first fly-eye lens 41 a.This means another fact that the light beams from each element of thesecond fly-eye lens 40 a are superposed on one element included by thefirst fly-eye lens 41 a. Therefore, the illuminance distribution on theincidental surface of the first fly-eye lens can be made uniform by anintegration effect. Each element included by the first fly-eye lens,thus made uniform, is further integrated (superposed) so as to be usedto irradiate the reticle 9. As a result, a satisfactory illuminanceuniformity can be realized on the reticle 9.

[0105] Furthermore, the focal depth of a projected image of the patternformed in a specific direction and having a pitch of the reticle pattern10 can be enlarged extremely because the first fly-eye lens groups 41 aand 41 b are positioned away from optical axis AX.

[0106] However, it is expected that the direction and the pitch of thereticle pattern 10 become different depending upon the employed reticle9. Therefore, it is preferable that the direction and the pitch are madeoptimum with respect to each reticle 9 by arranging the structure insuch a manner that the positions of the first fly-eye lens groups 41 aand 41 b and the guide optical systems 42 a, 42 b, 43 a and 43 b can bechanged or further the second fly-eye lens groups 40 a and 40 b and thelight dividing optical systems 20 and 21 can be changed by a drivesystem 56. The drive system 56 is operated in accordance with anoperation command issued from a main control system 50 in such a mannerthat the conditions, such as the position, are set in accordance with aninput made by a keyboard 54. As an alternative to this, a bar codereader 52 may be used to read a bar code pattern positioned on thereticle 9 so as to set the conditions in accordance with readinformation, or the aforesaid irradiation conditions may be written onthe bar code pattern on the reticle 9, or the main control system 50 maypreviously store (previously receive) reticle names and irradiationconditions corresponding to the reticles so as to determine theirradiation conditions by collating the reticle name written on the barcode pattern with the aforesaid contents stored by the main controlsystem 50.

[0107]FIG. 2 is an enlarged view which illustrates a portion from thelight dividing optical systems 20 and 21 shown in FIG. 1 to the firstfly-eye lens groups 41 a and 41 b. Assumptions are made here that thesurface of the first polyhedron prism 20 and that of the secondpolyhedron prism 21 facing each other are parallel to each other, andthe incidental surface of the prism 20 and the emission surface of theprism 21 are perpendicular to optical axis AX. The first polyhedronprism 20 is held by a holding member 22, while the second polyhedronprism 21 is held by a holding member 23. The holding members 22 and 23are held by a corresponding movable member group 24 a, 24 b and anothergroup 25 a and 25 b in such a manner that the holding members 22 and 23can be moved in a direction from right to left of the drawing sheet,that is along optical axis AX. The aforesaid operation is performed byactivating members 27 a, 27 b, 28 a and 28 b such as a motor. Since thefirst polyhedron prism 20 and the second polyhedron prism 21 are capableof individually moving, the interval between the two emitted light beamscan be radially changed while being centered at a point on optical axisAX by changing the interval between the two prisms 20 and 21.

[0108] A plurality of light beams emitted from the polyhedron prism 21are incident on the second fly-eye lens groups 40 a and 40 b. In thestructure shown in FIG. 2, a group consisting of one of the secondfly-eye lens groups, one of the first fly-eye lens groups, and one ofthe guide optical systems 42 and 43 is held by one of the correspondingholding member 44 a and 44 b. Since the holding members 44 a and 44 bare held by movable members 45 a and 45 b, they can be moved withrespect to the positions of stationary members 46 a and 46 b. Theaforesaid operation is performed by activating members 47 a and 47 b.

[0109] By integrally holding and moving the second fly-eye lens, thefirst fly-eye lens and the guide optical system, the positions of thelight beams emitted from the first fly-eye lens can be arbitrarilychanged in a plane perpendicular to optical axis AX while maintainingthe optically positional relationship between the first fly-eye lens andthe second fly-eye lens. It should be noted that members 48 a and 48 bprojecting from the holding members 44 a and 44 b are light shieldingplates. As a result, stray light beams generated by the light dividingoptical system can be shielded and a problem that unnecessary lightbeams reach the reticle can be prevented. Furthermore, the limit presentin the movable range for the holding members 44 a and 44 b can bereduced since the light shielding plates 48 a and 48 b are respectivelydeviated in the direction along optical axis AX.

[0110] Although the structure shown in FIG. 2 is arranged in such amanner that the position of each of the divided light beams can beradially changed with respect to optical axis AX by changing the opticalaxial directional interval between the light dividing optical systems(polyhedron prisms) 20 and 21, the directions in which light beam passmay be changed in concentrical directions relative to a position onoptical axis AX. FIG. 3 illustrates an embodiment in the aforesaid casein which the holding member 23 for holding the second polyhedron prism(the pyramid prism) 21 is held by a fixing member 25 and the holdingmember 23 can be rotated with respect to the fixing member 25 within thesurface of the drawing sheet drawn on FIG. 3A. The aforesaid rotation iscaused by a drive member 29 such as a motor provided for the fixingmember 29. Furthermore, a gear 30 is disposed adjacent to the holdingmember 23 to correspond to the position of the motor 29. FIG. 3B is across sectional view taken along an arrow 3A shown in FIG. 3A.

[0111] The fixing member 25 may be held as shown in FIG. 2 in such amanner that it is able to move in the direction of optical axis AX.Although FIG. 3 illustrates the case where the rotation is enabled withrespect to the second polyhedron prism 21, an arrangement may beemployed in which the rotation is also enabled with respect to the firstpolyhedron prism 20 (with respect to optical axis AX). As an alternativeto the structure in which the polyhedron prisms 20 and 21 areindividually rotated, the stationary members 26 a and 26 b shown in FIG.2 may be rotated with respect to another stationary member (for example,an exposure device or the like) relative to optical axis AX. In thiscase, the rotary mechanism may be arranged, for example, in such amanner that the holding member 23 shown in FIG. 3, in place of thepolyhedron prism 21, holds the stationary members 26 a and 26 b shown inFIG. 1.

[0112] As described above, in a case where the positions of a pluralityof the light beams emitted from the light dividing optical systems 20and 21 are radially or concentrically changed relative to optical axisAX, the positions of the second fly-eye lens groups 40 a and 40 b, onwhich the aforesaid light beams are incident, must be varied inaccordance with the changes in the positions of the light beams. FIG. 4illustrates an example of mechanism whereby a two dimensional (in adirection on a plane perpendicular to optical axis AX) operation can beperformed. FIG. 4 is a view which illustrates the members (the holdingmembers 44 a and 44 b) for integrally holding the second fly-eye lenses40 a and 40 b, the guide optical systems 42 a, 42 b, 43 a and 43 b andthe first fly-eye lenses 41 a and 41 b shown in FIG. 2, viewed from aposition adjacent to the reticle in a direction along optical axis AX.Synthetic fly-eye lenses 41A, 41B, 41C and 41D are held by correspondingholding members 44A, 44B, 44C and 44D which are held by movable members45A, 45B, 45C and 45D, the synthetic fly-eye lenses 41A, 41B, 41C and41D being able to radially move relative to optical axis AX byactivating members 46A, 46B, 46C and 46D. The activating members 46A,46B, 46C and 46D are able to move on the stationary members 49A, 49B,49C and 49D in directions substantially perpendicular to the aforesaidradial directions (in substantially concentric directions). Therefore,the synthetic fly-eye lenses 41A, 41B, 41C and 41D are able to betwo-dimensionally moved on the plane (on the surface of the drawingsheet) perpendicular to optical axis AX. As a result, the light beamsdivided by the light dividing optical system can be efficiently appliedto the reticle.

[0113] The directions in which the movable members 45A, 45B, 45C and 45Dshown in FIG. 4 are removed are not limited to the radial directionsrelative to optical axis AX. The directions may be arbitrary directionsperpendicular to optical axis AX. Also in a case where a system can beonly moved one-dimensionally as shown in FIG. 2, the directions may bearbitrary directions perpendicular to optical axis AX.

[0114]FIG. 5 illustrates a modification of the guide optical system,wherein all of the guide optical systems 42 a, 42 b, 43 a and 43 b aredisposed eccentrically with respect to the centers of the second fly-eyelenses 40 a and 40 b and the first fly-eye lenses 41 a and 41 b.

[0115] The positions of irradiation light beams emitted from the secondfly-eye lenses 40 a and 40 b are changed on the plane perpendicular tooptical axis AX by the eccentric guide optical systems 42 a, 42 b, 43 aand 43 b before the irradiation light beams are incident on the firstfly-eye lenses 41 a and 41 b.

[0116] Furthermore, the positions (the positions on the planeperpendicular to optical axis AX) of the light beams on the incidentalsurfaces of the first fly-eye lens groups 41 a and 41 b can be changedby changing the degree of eccentricity of the guide optical systems 42a, 42 b, 43 a and 43 b. The structure shown in FIG. 5 is arranged insuch a manner that the change of the eccentricity amount is performed byactivating members 421 a, 421 b, 431 a and 431 b. The activating members421 a, 421 b, 431 a and 431 b enable the guide optical systems 42 a, 42b, 43 a and 43 b via holding members 420 a, 420 b, 430 a and 430 b. Theincidental surfaces (the left end portion of the drawing) of the secondfly-eye lenses 40 a and 40 b and the incidental surfaces (the left endportion of the drawing) of the first fly-eye lenses 41 a and 41 b hold asubstantially image forming relationship. The aforesaid image formingrelationship (in a direction along optical axis AX) cannot be out oforder if the operations of the guide optical systems 42 a, 42 b, 43 aand 43 b are performed on the plane perpendicular to optical axis AX.Also the first fly-eye lenses 41 a and 41 b are, similarly to the guideoptical members, able to move in a direction on the plane perpendicularto optical axis AX by activating members 411 a and 411 b.

[0117] In the system shown in FIG. 5, the light beams emitted from thesecond fly-eye lenses 40 a and 40 b can be moved to arbitrary positionson the plane perpendicular to optical axis AX by the guide opticalsystems 42 a, 42 b, 43 a and 43 b. Therefore, the second fly-eye lensgroups 40 a and 40 b and the light dividing optical systems 20 and 21may be stationarily disposed in place of the arrangement in which theyare able to move. In the structure shown in FIG. 5, the aforesaidelements are held by a common holding member 22 a. In a case where thearrangement is made to comprise, as shown in FIG. 5, the guide opticalsystems 42 a, 42 b, 43 a and 43 b and the first fly-eye lens groups 41 aand 41 b, the light dividing optical systems 20 and 21 and the secondfly-eye lens groups 40 a and 40 b may be arranged to be movable as shownin FIGS. 2 and 3. Although the structure shown in FIG. 5 is arranged insuch a manner that both the first and the second fly-eye lensesrespectively comprise two lenses, the number can be arbitrarilydetermined.

[0118]FIGS. 6, 7 and 8 illustrate modifications of the light dividingoptical system. The structure shown in FIG. 6 is composed of concavepolyhedron prism 20 a and a convex lens (or a lens group having positivepower) 21 a. Irradiation light beams emitted from an input lens 4 aredivided and scattered by the polyhedron prism 20 a, and then they aregathered by the convex lens 21 a so that they are incident on the secondfly-eye lenses 40 a and 40 b. It should be noted that change of theangle θ1 of inclination of the inclined surface of the polyhedron prism20 a will, at the positions adjacent to the second fly-eye lenses 40 aand 40 b, enable the positions of the divided light beams to be changedon the plane perpendicular to optical axis AX. For example, anarrangement may be employed in which two polyhedron prisms 20 a and 20 bhaving individual inclination angles θ1 and θ2 are used in such a mannerthat they can be interchanged by an activating member 27 c. In the abovementioned structure, the two polyhedron prisms 20 a and 20 b are held byan integrated holding member 22 a which is held by a movable member 24c. The movable member 24 c is able to move with respect to a stationarymember 26 c by the power of an activating member 27 c.

[0119] Although the two polyhedron prisms shown in FIG. 6 are arrangedin such a manner that they have the inclined surfaces having individualangles but formed in the same direction, the directions may be differentfrom each other. As an alternative to this, either of them may have abisectioning V-shape recess and the residual one a pyramid recess. Themechanism for holding the second fly-eye lens groups 40 a, 40 b, theguide optical systems 42 a, 42 b, 43 a and 43 b and the first fly-eyelens groups 41 and 41 b is formed similarly to those shown in FIGS. 2, 4and 5.

[0120]FIG. 7 illustrates an example in which an optical fiber 20 c isused as the light dividing optical system. Irradiation light beamsincident on an incidental portion 20 b of a fiber are divided into twosections by emitting portions 21 b and 21 c. The emitting portions 21 band 21 c are held by holding members 44 c and 44 d which also integrallyhold the synthetic fly-eye lens shown in FIG. 2. Hence, the positions ofthe light beams can automatically be moved caused to follow) when thesynthetic fly-eye lenses re moved.

[0121]FIG. 8 illustrates an example in which a plurality of mirrors 20d, 21 e and 21 f are used as the light dividing optical system. A firstmirror 20 d is a V-shape mirror for dividing the light beams into twosections. Second mirrors 21 e and 21 f are flat mirrors for introducingthe light beams into the first fly-eye lenses 40 a and 40 b. Thisexample is arranged in such a manner that the second mirrors 21 e and 21f are integrally held by holding members 44 e and 44 f which integrallyhold the synthetic fly-eye lens.

[0122] In the two examples shown in FIGS. 7 and 8, the holding members44 c, 44 d, 44 e and 44 f for holding the lenses are able to move on aplane in a direction perpendicular to optical axis AX similarly to FIG.2 or 4. The number of the fly-eye lenses and the number of the dividedsections divided by the light dividing optical system are not limited totwo and are therefore determined arbitrarily. In the structure shown inFIG. 7, the number of the divided sections of the fiber 20 c may bechanged, while a pyramid mirror (dividing into four sections) may beemployed as the first mirror 20 d in the structure shown in FIG. 8.

[0123] The structure of the light dividing optical system is not limitedto the aforesaid description. or example, diffraction gratings, inparticular, phase diffraction gratings, or a convex lens array can beused in place of the polyhedron prisms 20 a and 20 b shown in FIG. 6.

[0124]FIG. 9 illustrates a modification of the system from the firstfly-eye lens groups 41 a and 41 b to the projection optical system 11.Irradiation light beams emitted from the emission surface of the firstfly-eye lens, that is, from the Fourier transformed surface with respectto the reticle pattern 10, are gathered and shaped by a relay lens 6 a.At this time, a plane which holds an image forming relationship with thereticle pattern 10 is formed by the action of the relay lens 6 a.Therefore, the irradiation area on the surface of the reticle patterncan be limited by disposing a visual field diaphragm (irradiation areadiaphragm) 14 on the aforesaid plane.

[0125] Irradiation light beams are applied to the reticle 9 via a relaylens 6 b, a condenser lens 6 c and 8 and a mirror disposed consecutivelyto the visual field diaphragm 14. Furthermore, a Fourier transformedsurface 17 b of the reticle pattern 10 appears between the relay lens 6b and the condenser lens 6 c.

[0126] Although an aperture diaphragm 5 shown in FIG. 9 is disposedadjacent to the emission side of the second fly-eye lens, it may bedisposed adjacent to the Fourier transformed surface 17 b.

[0127] Elements of the fly-eye lens for use in the structure accordingto the present invention will now be described with reference to FIG.10. FIG. 10A illustrates the aforesaid structure in which the incidentalsurface 401 a, the light source side focal plane 403 a, the emissionsurface 402 a and the reticle side focal surface 404 a coincide with oneanother.

[0128] However, in the structure shown in FIG. 10A, all of theirradiation light beams in the element of the fly-eye lens pass througha glass element and a light converged point is generated in the glass(fly-eye lens). In a case where a pulse laser such as an excimer laseris used as the light source, energy per pulse becomes excessively largeand therefore there arises risk of breakage of the glass element by theoptical energy in the converged point if the converged point is presentin the glass element.

[0129]FIGS. 10B and 10C respectively illustrate examples of the fly-eyelenses for preventing the aforesaid problem. FIG. 10B illustrates astructure in which both an incidental surface 401 b and an emissionsurface 402 b are made of the surfaces of a convex lens, and a reticleside focal surface 404 b is different from an emission surface 402 b (alight source side focal surface 403 b and an incidental surface 401 bcoincide with each other). The aforesaid arrangement can be realized bychanging the curvature of the incidental surface 401 b and that of theemission surface 402 b from each other. As a result, the light beamsemitted from the light source are converged at a point outside thefly-eye lens element 400 b.

[0130]FIG. 10C illustrates a modification of the structure shown in FIG.10B, where a fly-eye lens element 400 c has a flat incidental surface401 c. Also in this case, the converged point (a reticle side focalsurface 404 c) can be located outside the lens 400 c. Furthermore, thelight beams are not gathered in the lens 400 c. However, the light beamsexcept for vertical and parallel beams come in contact with the innerwall of the fly-eye lens 400 c and therefore stray beams are generatedbecause the incidental surface 401 c has no refraction effect.Therefore, the structure shown in FIG. 10C will enable an excellenteffect to be obtained as the second fly-eye lens in a case where thelight source comprises the laser beam source. The reason for this liesin that use of the laser beam source will enable the incidental lightbeams to be parallel beams and to be perpendicularly incident on thefirst fly-eye lens.

[0131] On the contrary, the structure shown in FIG. 10B is suitable whenit is used as the first fly-eye lens in a case where the light source isthe laser beam similarly to the structure shown in FIG. 10C.

[0132] A fly-eye lens element shown if FIG. 10D is composed of twoconvex lenses 400 d and 400 e. The structure is arranged to be differentfrom those shown in FIGS. 10A to 10C in such a manner that a spacebetween the two convex lenses 400 d and 400 e is filled with air ornitrogen or helium gas. In a case where an exposure wavelength of 200 nmor less is used, it is preferable that the volume of a transmissivesolid portion made of, for example, glass be minimized as shown in FIG.10D because a proper lens material having satisfactory transmissivitycannot be available. In this case, it is preferable to constitute theprojection optical system by a reflecting optical system (a refractivemember may be partially employed) and also the light dividing opticalsystem may use a reflecting mirror arranged as shown in FIG. 8.

[0133] A method of optimizing the aforesaid systems to correspond to thereticle pattern to be exposed will now be described. It is preferablethat the position (the position on the plane perpendicular to theoptical axis) of each first fly-eye lens group be determined (changed)in accordance with the reticle pattern to be transferred. In this case,the position may be determined as described above in such a manner thatthe irradiation light beams from the first fly-eye lens groups areincident on the reticle pattern at a position at which the optimumresolution and an effect of improving the focal depth can be obtainedwith respect to the precision (pitch) of the pattern to be transferred.

[0134] Specific examples of determining the positions of each firstfly-eye lens group will now be described with reference to FIGS. 11 and12A to 12D. FIG. 11 is a view which schematically illustrates a portionfrom the first fly-eye lens groups 41 a and 41 b to the reticle pattern10. In the structure shown in FIG. 11, reticle side focal surfaces 414 aand 414 b of the first fly-eye lens group 41 coincide with the Fouriertransformed surface 17 of the reticle pattern 10. A lens or a lens groupwhich cause the two elements to hold the Fourier transformationrelationship is expressed by one lens 6. Furthermore, an assumption ismade that both of the distance from the principal point of the lens 6facing the fly-eye lens to the reticle side focal surfaces 414 a and 414b of the fly-eye lens group 41 and the distance from the principal pointof the lens 6 facing the reticle to the reticle pattern 10 are f.

[0135]FIGS. 12A and 12C illustrate an example of a portion of a patternto be formed in the reticle pattern 10. FIG. 12B illustrates a positionon the Fourier transformed surface 17 (on the pupil surface of theprojection optical system) at the center of the first fly-eye lens groupwhich is most suitable in the case of the reticle pattern shown in FIG.12A. FIG. 12D illustrates the positions (the positions of the centers ofthe optimum fly-eye lens groups) of the fly-eye lens groups which aremost suitable in the case of the reticle pattern shown in FIG. 12C.

[0136]FIG. 12A illustrates a so-called one-dimensional line-and-spacepattern in which transmissive portions and light shielding portions arearranged in direction Y while having the same width and furthermore theyare regularly arranged in direction X at pitch P. At this time, theoptimum positions for each first fly-eye lens are, as shown in FIG. 12B,arbitrary points on line segments Lα and Lβ assumed on the Fouriertransformed surface. FIG. 12B is a view which illustrates the Fouriertransformed surface 17 with respect to the reticle pattern 10 whenviewed in a direction of optical axis AX, wherein coordinate system Xand Y on the surface 17 is made to be the same as that of FIG. 12A whichillustrates the reticle pattern when viewed in the same direction.

[0137] Referring to FIG. 12B, the distances α and β from center C,through which optical axis AX passes, to line segments Lα and Lβ hold arelationship expressed by α=β which is equal to f·(½)·(λ/p). Expressingthe distances α and β by f·sin Φ, sin Φ=λ/2P coincides with theaforesaid value. Therefore, if each center (each center of gravity ofthe light quantity distribution of secondary light source images each ofwhich is formed by the first fly-eye lenses) is positioned on linesegments Lα and Lβ either o ±1-order diffracted light beams generatedfrom the irradiation light beams from each fly-eye lens and 0-orderdiffracted light beam pass through positions of a line-and-space patternshown in FIG. 12A which are the same distance from optical axis AX onthe pupil surface 12 of the projection optical system 11. Hence, thefocal depth with respect to the line-and-space pattern (see FIG. 12A)can be made largest and therefore high resolution can be obtained.

[0138]FIG. 12C illustrates a case where the reticle pattern is aso-called isolated space pattern, wherein the X-directional (in thelateral direction) pitch of the pattern is Px and the Y-directional (inthe longitudinal direction) pitch of the same is Py. FIG. 12D is a viewwhich illustrates the optimum position for each first fly-eye lens inthe aforesaid case, wherein the positional and rotational relationshipwith FIG. 12C are the same as that between FIG. 12A and 12B. When theirradiation light beams are incident on the two-dimensional patternarranged as shown in FIG. 12C, diffracted light beams are generated inthe two-dimensional direction which corresponds to the periodicity inthe two-dimensional direction of the pattern. Also in thetwo-dimensional pattern arranged as shown in FIG. 12C, the focal depthcan be made maximum by causing either of the ±1-order diffracted lightbeams and the 0-order diffracted light beams to be the same distancefrom optical axis AX on the pupil surface 12 of the projection opticalsystem 11. Since the pitch in the direction X is Px in the pattern shownin FIG. 12C, a maximum focal depth of the X-directional component of thepattern can be obtained if the center of each fly-eye lens is positionedon the line segments Lα and Lβ which hold the relationshipα=β=f·(½)·(λ/Px). Similarly, if the center of each fly-eye lens ispresent on line segments Lγ and Lε which hold the relationshipsγ=εf·(½)·(λ/Py), the maximum focal depth of the Y-directional componentof the pattern can be obtained.

[0139] As described above, when the irradiation light beams from thefly-eye lens groups disposed at the positions shown in FIG. 12B or 12Dare incident on the reticle pattern 10, 0-order diffracted light beamcomponent Do and either +1-order diffracted light beam component DR or−1-order diffracted light beam component Dm pass through the opticalpath on the pupil surface 12 in the projection optical system 11 at thesame distance from optical axis AX. Therefore, a projection exposureapparatus revealing high resolution and a large focal depth can berealized.

[0140] Although only the two examples as illustrated in FIGS. 12A and12C have been considered as the reticle pattern 10, another pattern maybe used in such a manner that the center of each fly-eye lens is locatedat a position which causes either of +1-order or −1-order diffractedlight beam component from the pattern and the 0-order diffracted lightbeam component to pass through the optical path which is located atsubstantially the same distance from optical axis AX on the pupilsurface 12 in the projection optical system. In the example of thepattern shown in FIGS. 12A and 12C, the ratio (duty ratio) of the lineportion and the space portion is 1:1, and therefore ±1-order diffractedlight beams become intensive. Hence, attention is paid to the positionalrelationship between either of the ±1-order diffracted light beams andthe 0-order diffracted light beam. However, in a case where the dutyratio of the pattern is not 1:1 or the like, an arrangement may beemployed in which the positional relationship between another diffractedlight beam, for example, either of ±2-order diffracted light beams andthe 0-order diffracted light beam are allowed to pass through thepositions distant, by the same distance, from optical axis AX on thepupil surface 12 of the projection optical system.

[0141] In a case where the reticle pattern 10 has, as shown in FIG. 12D,the two-dimensional cyclic pattern, a high order diffracted light beamcomponent higher than 1-order distributed in direction X (in the firstdirection) with respect to one of the 0-order diffracted light beamcomponents and a high order diffracted light beam component higher than1-order distributed in direction Y (in the second direction) can bepresent on the pupil surface 12 of the projection optical system whenattention is paid to a specific 0-order diffracted light beam component.Assuming that the image of a two-dimensional pattern is satisfactorilyformed with respect to one specific 0-order diffracted light beamcomponent, it is necessary for the position of a specific 0-orderdiffracted light beam component (one of the first fly-eye lenses) to beadjusted in such a manner that the three components consisting of one ofthe high-order diffracted light beam component distributed in the firstdirection, one of the same distributed in the second direction and thespecific 0-order diffracted light beam component are distributed by thesame distance from optical axis AX on the pupil surface. For example, itis preferable that the center of the first fly-eye lens be made coincidewith any one of points Pζ, Pη, Pκ and Pμ. Since all of the points Pζ,Pη, Pκ and Pμ are intersections of line segment Lα or Lμ (the optimumportion in terms of the periodicity in the direction X, that is, theposition at which the 0-order diffracted light beam and either of the±1-order diffracted light beam in the direction X are spaced by the samedistance from the optical axis on the pupil surface 12 of the projectionoptical system) and line segments Lγ and Lε (the optimum position interms of the periodicity in the direction Y), the aforesaid position isthe optimum position in either of the directions X and Y.

[0142] Although the description has been given while assuming a twodimensional pattern having the two-dimensional directionality at thesame point on the reticle, the aforesaid method can be adapted to a casewhere a plurality of patterns having different directionalities arepresent in the same reticle pattern.

[0143] In a case where the pattern on the reticle has a plurality ofdirectionalities or precisions, the optimum positions for the fly-eyelens groups are the positions which correspond to the directionality ofeach pattern and the precision. As an alternative to this, the firstfly-eye lens may be disposed at the mean position of the optimumpositions. The aforesaid mean position may be the mean load positionobtained by adding weight to the precision or the significance of thepattern.

[0144] The 0-order light beam components emitted from the first fly-eyelens are incident on the wafer while being inclined with respect to thewafer. In this case, a problem arises in that the position of thetransferred image is undesirably shifted in a direction on the wafer atthe time of finely defocusing the wafer 13 if the direction of thecenter of gravity of the light quantities of (a plurality of) theinclined incident light beams is not perpendicular to the wafer. Inorder to prevent this, the direction of the center of gravity of thelight quantities on the image forming surface or on its adjacent surfacemust be perpendicular to the wafer, that is, in parallel to optical axisAX.

[0145] That is, assuming an optical axis (the center line) for eachfirst fly-eye lens, the vector sum of the product of the position vectoron the Fourier transformed surface of the optical axis (the center line)with respect to optical axis AX of the projection optical system 11 andthe light quantity emitted from each fly-eye lens must be zero.

[0146] A further simple method may be employed in which 2 m (m is anatural number) first fly-eye lenses are used, the positions of m firstfly-eye lenses are determined by the aforesaid optimizing method (seeFIG. 12) and the residual m first fly-eye lenses are disposedsymmetrical to optical axis AX. The detailed description about theaforesaid structure has been disclosed in U.S. patent Ser. No. 791,138(filed on Nov. 13, 1991).

[0147] As described above, when the position of each first fly-eye lensis determined, the position (see FIG. 5) of the guide optical system andthe state (see FIGS. 2, 3 and 6) of the light dividing optical systemare determined. The positions and the like of the guide optical system,the light dividing optical system or the second fly-eye lens must bedetermined so as to cause the irradiation light beams to be incident onthe first fly-eye lens most efficiently (in such a manner that the lightquantity loss can be prevented).

[0148] In the aforesaid system, it is preferable that each movingportion has a position detector such as an encoder. The main controlsystem 50 or the drive system 56 shown in FIG. 1 moves, rotates andexchanges each element in accordance with position information suppliedfrom the aforesaid position detector. As for the shape of the lenselement for each fly-eye lens group, the effective area of the reticleor the circuit pattern area are mainly in the form of a rectangle.Therefore, only the pattern portion of the reticle can be efficientlyirradiated with light beams in a case where the incidental surface(which holds an image forming relationship with the reticle patternbecause the emission surface and the surface of the reticle pattern holdthe Fourier transformed relationship and also the incidental surface(light source side focal surface) and the emission side (reticle sidefocal point) hold the Fourier transformed relationship) of each elementof the first fly-eye lens is formed into a rectangular shape tocorresponding to the planar shape of the reticle pattern.

[0149] The number of the incidental surfaces of the first fly-eye lens(composed of the aforesaid elements) may be determined arbitrarily. Inthis case, the light quantity loss can be reduced by forming the totalincidental surface into a shape similar to that of the incidentalsurface of one element of the second fly-eye lens. For example, thetotal incidental surface of each first fly-eye lens is made to arectangular shape in a case where the incidental surface of one elementof the second fly-eye lens is formed into a rectangular shape. In a casewhere the incidental surface of one element of the second fly-eye lensis formed into a regular hexagon, the total incidental surface of eachfirst fly-eye lens is formed into a shape which is inscribed in theregular hexagon.

[0150] In a case where the image of the shape of the incidental surfaceof one element of the second fly-eye lens is projected by the guideoptical system in such a manner that it is somewhat larger than thetotal incidental surface of each first fly-eye lens, the effect ofmaking irradiation uniform at the first fly-eye lens can be furtherimproved. As for the size of the emission surface of each first fly-eyelens, it is preferable that the number of apertures (a single width ofthe angle distribution on the reticle) per one emitted light beam beabout 0.1 to about 0.3 with respect to the reticle side number ofapertures of the projection optical system. If it is smaller than 0.1times, the correctivity of the pattern transference deteriorates. If itis larger than 0.3 times, an effect of improving the resolution and thatof realizing a large focal depth cannot be obtained.

[0151] The apparatus according to the aforesaid embodiment may bearranged in such a manner that the first fly-eye lens groups, the guideoptical system and the second fly-eye lens groups (the structure shownin FIG. 2) following the light divider can be exchanged for a portionwhich corresponds to a conventional irradiation optical system, that is,a structure formed by integrating the relay lens and one fly-eye lens.

[0152] The first embodiment employs a pyramid type prism arranged asshown in FIG. 3 as a light divider for dividing the irradiation lightbeams emitted from the light source into four portions. However, anotherlight divider except for the pyramid type prism and arranged, forexample, as shown in FIG. 15 may be used. The light divider shown inFIG. 15 comprises a polyhedron prism (a first prism) 50 having aV-shaped concave, a prism (a second prism) formed by combining apolyhedron prism 51 having a V-shaped convex and a polyhedron prism 20having a V-shaped concave, and a polyhedron prism (a third prism) havinga V-shaped convex. That is, two pairs of light dividers, each of whichis composed of two V-shaped prisms and which are used in the firstembodiment (see FIG. 2), are arranged in series. Therefore, theirradiation light beams emitted from the light source 1 are divided intofour light beams by the refraction effect of the aforesaid four prisms.Hence, the light beams are incident on corresponding second fly-eyelenses 40 a to 40 d (FIG. 1 shows only those 40 a and 40 b).

[0153] The first light dividers 50 and 51 divide the irradiation lightbeams emitted from the light source 1 while making them substantiallysymmetrical with respect to the direction Y and causing them to havesubstantially the same light quantity. Furthermore, the first lightdividers 50 and 51 emit the two divided light beams in such a mannerthat they travel in parallel to each other (substantially in parallel tooptical axis AX) while being positioned away from each other by apredetermined interval (which corresponds to the X-directional intervalbetween the center of the first fly-eye lens 41 a and that of 41 d orbetween those 41 b and 41 c on the pupil surface with respect to thedirection X). On the other hand, the second light dividers 20 and 21divide the two light beams divided by the first light dividers 50 and 51while making them substantially symmetrical with respect to thedirection X and causing them to have substantially the same lightquantity. Furthermore, the second light dividers 20 and 21 emit the fourlight beams in such a manner that they travel substantially in parallelto one another (substantially in parallel to optical axis AX) whilebeing positioned away from one another by a predetermined interval(which corresponds to the Y-directional interval between the center ofthe first fly-eye lens 41 a and that of 41 b or between those 41 c and41 d on the pupil surface with respect to the direction Y).

[0154] Furthermore, the prisms 50 (51 and 20) and 21 are arranged so asto be capable of individually moving along optical axis AX (in adirection Z in case of FIG. 15). Therefore, by adjusting the interval byrelatively moving the first prism 50 and the second prism (51 and 20) inthe direction of the optical axis, the X-directional interval betweenthe two light beams emitted from the polyhedron prism 20 can bedetermined to be an arbitrary value. Similarly, by adjusting theinterval between the second prism (51 and 20) and the third prism 21 byrelatively moving them in the direction of the optical axis, theY-directional interval between the two pairs of two light beams emittedfrom the third prism 21 can be determined to be an arbitrary value.

[0155] There is sometimes a necessity of slightly moving the third prism21 in the direction of the optical axis when the optical directionalinterval between the first prism 50 and the second prism (51 and 20) ischanged because the polyhedron prisms 51 and 20 are integrally formedwith each other. Although the polyhedron prisms 51 and 20 are integrallyformed by adhesion, an arrangement may be employed in which they areable to individually move in the direction of the optical axis.

[0156] As described above, in order to optimize the irradiationcondition (in other words, the position of the center of each of thefour pairs of the first fly-eye lenses on the pupil surface) inaccordance with the precision (the pitch, the linear width, the periodand the direction) of the pattern for each reticle, the position and thelike of the four pairs of the first fly-eye lenses 41 a to 41 d can beshifted by the drive system. Therefore, in order to cause the four lightbeams emitted from the third prism to be correctly incident on thesecond fly-eye lenses 40 a to 40 d when the four sets of the firstfly-eye lenses 41 a to 41 d are moved in accordance with the precisionof the reticle pattern, the three prisms 50, (51 and 20) and 21 areindividually moved in the direction of the optical axis insynchronization (while following) with the aforesaid movement.

[0157] An arrangement may be employed in which three prisms 50, (51 and20) and 21 are made rotative relative to optical axis AX depending uponthe positions of four sets of the first fly-eye lenses 41 a to 41 d onthe pupil surface 17 so as to be rotated in synchronization with themutual adjustment of the three prisms in the optical axial direction sothat the four light beams are incident on the second fly-eye lenses 40 ato 40 d. Another arrangement may be employed in which the three prismsare integrally constituted on a plane (plane XY of FIG. 15)perpendicular to optical axis in such a manner that they can betwo-dimensionally moved so as to be relatively moved with respect to theirradiation light beams emitted from the light source on a planeperpendicular to optical axis AX, so that the light quantities of thefour light beams emitted from the third prism are finely adjusted so asto be substantially the same. In this case, it is preferable that thelight quantity of each of the four light beams to be applied to thereticle 9 is detected by a photoelectric detector and the aforesaidrelative movement is controlled in accordance with the result of thedetection. As an alternative to the arrangement in which the threeprisms are moved, an arrangement may be employed in which the positionof the irradiation light beam to be incident on the first prism 50 isfinely moved by, for example, inclining the parallel and flat glassdisposed between the input lens 4 (FIG. 1) and the first prism 50.

[0158]FIG. 16 is an enlarged view which illustrates a portion from thelight divider to the first fly-eye lenses 41 a to 41 d in a case wherethe light divider shown in FIG. 15 is used in the projection exposureapparatus (see FIG. 1). Assumptions are made here that the facingsurfaces of the first prism 50 between the prism 51 and those betweenthe prism 20 and the third prism 21 run parallel to each other, and theincidental surface of the first prism 50 and the emission surface of thethird prism 21 are perpendicular to each other. In addition, the joinedsurfaces of the second prisms 51 and 20, that is, the emission surfaceof the prism 51 and the incidental surface of the prism 20 areperpendicular to optical axis AX. Referring to FIG. 16, the samereference numerals as those shown in FIG. 2 are given the same referencenumerals and their descriptions are omitted here.

[0159] The first prism 50 is held by the holding member 60, the secondprism (51 and 20) is held by the holding member 22, and the third prism21 is held by the holding member 23. As an alternative to applying theprism 51 and 20 to each other, they may be simply hermetically held orstationarily held while positioning them away from each other by apredetermined interval. The holding member 60 is held by movable members61 a and 61 b in such a manner that they are able to move on stationarymembers 26 a and 26 in a direction from right to left when viewed in thedrawing, that is, in a direction along optical axis AX. The aforesaidmovement is enabled by activating members 62 a and 62 b such as motors.

[0160] Since the first to third prisms 50, (51 and 20) and 21 are ableto move individually, the X-, and Y-directional intervals between thefour light beams emitted to be emitted can be individually adjusted byarbitrarily changing the mutual distances between the three prisms inthe direction of the optical axis. Hence, the positions of the fourlight beams can be arbitrarily, for example, can be radially changedrelative to optical axis AX on a plane perpendicular to optical axis AX.For example, in a case where the reticle pattern 10 is a two-dimensionalcyclic pattern and as well having different X- and Y-directionalpitches, the centers of the four sets of the first fly-eye lenses must,on the pupil surface 17, coincide with the vertex of the rectanglerelative to optical axis AX. Also in this case, by adjusting the mutualintervals between the three prisms 50, (51 and 20) and 21, the fouremitted light beams are enabled to be accurately incident on thecorresponding second fly-eye lenses 40 a to 40 d. Furthermore, the fouremitted light beams can be shifted in the concentric directions relativeto optical axis AX by arranging the structure in such a manner that thethree prisms 50, (51 and 20) and 21 can be rotated relative to opticalaxis AX as described above.

[0161] Although four sets of the fly-eye lenses are used in thestructure shown in FIG. 15, it is sufficient to use two sets of fly-eyelenses in a case where the reticle pattern is a one-dimensional cyclicpattern for example. In this case, two sets of fly-eye lenses areselected from the four sets and the centers of the two fly-eye lensesare made substantially coincide with positions deviated from opticalaxis AX by a quantity corresponding to the precision of the reticlepattern.

[0162] Furthermore, the three prisms are moved in accordance with thepositions of the two second fly-eye lenses, thus selected, in such amanner that the two prisms are brought into contact with each other in ahermetical manner so as to make either of the distance from the firstprism 50 to the second prism (51 and 20) or the distance from the secondprism (51 and 20) to the third prism 21 to be zero. In a case where thesecond fly-eye lenses 40 a and 40 b are located substantially symmetricwith respect to optical axis AX and as well as distant from each otherby a predetermined distance in the direction X, the second prism (51 and20) and the third prism 21 are brought into contact with each other in ahermetical manner so as to make the distance to be zero.

[0163] As a result, the irradiation light beams emitted from the lightsource 1 are divided into two portions by the first prism 50 and thesecond prism, that is the prism 51 and the irradiation light beams arenot divided by the prism 20 and the third prism 21. Hence, theirradiation light beams emitted from the light source 1 are divided intotwo portions by the three prisms while preventing the light quantityloss and they are respectively and collectively incident on the two setsof the second fly-eye lenses even if only the two sets of the fly-eyelenses are used.

[0164] In a case where a reticle which is not adapted to the inclinedirradiation method, for example, a phase shift reticle of a spatialfrequency modulation type, is used, the irradiation must be performed insuch a manner the light quantity distribution of the irradiation lightbeams on the pupil surface 17 must be limited to a circular (or arectangular) region around the optical axis AX. In this case, the prismsare moved so that the first prism 50 and the second prism (51 and 20),and the second prism (51 and 20) and the third prism 21 are respectivelyare hermetically held so as to make the interval in the direction ofoptical axis AX to be zero. Furthermore, the four sets of the fly-eyelenses are moved so as to be integrated relative to optical axis AX. Asa result, the irradiation light beams emitted from the light source 1are not divided by the three prisms 50, (51 and 20) and 21 but they canbe incident on the four integrated fly-eye lenses while preventing thelight quantity loss. Hence, even if the light divider shown in FIG. 15is used, the conventional irradiation (hereinafter called an “ordinaryirradiation”) can be employed. In a case where the four sets of thefly-eye lenses must be moved and integrated (combined), it is preferablethat four sets of holding members be structured in such a manner thatthe four sets of the holding members for integrally holding the firstand the second fly-eye lenses and the guide optical system will not forma gap between contact portions of the four sets of the first fly-eyelenses.

[0165] As can be understood from above, the inclined irradiation and theordinary irradiation can easily be changed over while eliminating thenecessity of, for example, changing the optical member in a case wherethe light divider shown in FIG. 15 is used. In case of the inclinedirradiation, switching can easily be performed between the case in whichthe four sets of the fly-eye lenses are used and the case where the twosets of the fly-eye lenses are used. If a zoom lens system is disposedbetween the input lens 4 and the first prism 50, for example, and aswell if the diameter (the area) of the irradiation light beam to beincident on the first prism 50 can be varied, the light quantity losscan be prevented furthermore and a problem which takes place in that thelight beams emitted from the third prism 21 are concentrically incidenton a portion of the incidental surface of the second fly-eye lens can beprevented. In a case where the four sets of the fly-eye lenses areradially moved relative to optical axis AX for example, a necessitysimply lies in that the diameter of the irradiation light beam to beincident on the first prism 50 is adjusted by the zoom lens system inaccordance with the size (the X- and Y-directional widths) of theincidental surface of each second fly-eye lens. Furthermore, if a zoomlens of the aforesaid type is used, the coherence factor (value) of theirradiation optical system can be varied at the time of performing theordinary irradiation.

[0166] A second embodiment of the projection exposure apparatus will nowbe described with reference to FIGS. 17 and 18. FIG. 17 is a view whichillustrates the schematic structure of the projection exposure apparatusaccording to this embodiment. FIG. 18 is an enlarged view whichillustrates a portion from the light dividers 20 and 21 to the firstfly-eye lenses 41 a and 41 b. Referring to FIGS. 17 and 18, the sameelements as those shown in FIGS. 1 and 2 are given the same referencenumerals and their descriptions are omitted here.

[0167] As shown in FIG. 17, this apparatus according to this embodimentuses, as the exposure light source, a KrF or ArF excimer laser orharmonic waves such as a metal vapor laser or YAG laser. Therefore, thespeckle interference fringes are prevented and the illuminanceuniformity on the wafer is improved by disposing an optical pathdifference generating member (for example, a parallel and flat glass) 70in the irradiation optical system. The above mentioned arrangement isdifferent from the first embodiment (see FIG. 1) and therefore thedescription will now be given about it. It should be noted that a beamshaping optical system 81 shown in FIG. 17 includes a beam expander andthe like and capable of shaping the cross section of the light beam intoa proper shape (which is in the form of a square in usual).

[0168] As shown in FIG. 17, the parallel and flat glass 70 serving asthe optical path difference generating member is disposed in either ofthe optical paths (in the structure shown in FIG. 17, the optical pathfor the light beam to be incident on the second fly-eye lens group 40 a)for the light beams divided by the light dividers 20 and 21. Therefore,the light beam to be incident on the second fly-eye lens 40 a is given aphase delay by a predetermined quantity from the light beam to beincident on the second fly-eye lens group 40 b. That is, an optical pathdifference is generated between the two light beams. This embodiment isarranged in such a manner that the thickness of the parallel and flatglass 70 is determined so as to make the optical path difference betweenthe two light beams to be longer than a coherent length LS (LS=λ2/Dl).Although the parallel and flat glass 70 is disposed in the optical pathfor either of the two light beams, the parallel and flat glass may bedisposed in each of the optical paths if the optical path differencebetween the two light beams is always longer than the coherent lengthLS. Furthermore, the optical path difference generating member may be,for example, a mirror in. place of the parallel and flat glass if it iscapable of turning the light beam to give an optical path difference.

[0169] The optical path difference generating member is not limitedparticularly if it is able to give a proper phase difference between thelight beams. The number of the optical paths may be the same number asor a number smaller than the number of the second fly-eye lens groups byone in order to cause a plurality of light beams divided by the lightdivider to have different optical path differences (longer than thecoherent length). For example, in a case where four second fly-eye lensgroups are disposed, the light divider is composed of the firstpolyhedron prism 20 having a pyramid concave and the second polyhedronprism 21 having a pyramid convex (see FIG. 3). Furthermore, four (orthree) parallel and flat glass each having an individual thickness tocorrespond to the coherent length LS may be disposed in the opticalpaths of the light beams in order to cause the four light beams to havedifferent phase differences (optical path differences). The pyramid typeprism may be replaced by a light divider arranged as shown in FIG. 15.

[0170] The parallel and flat glass 70, as shown in FIG. 18, is held bythe holding member 44 a integrally with the first and second fly-eyelenses 41 a, 40 a, and the guide optical systems 42 a and 43 a.Therefore, when the first fly-eye lens is shifted in accordance with theprecision, the parallel and flat glass 70 is also moved.

[0171] An arrangement may be employed in which the parallel and flatglass 70 is not secured to the holding member 44 a but it is made to beindividually movable so as to drive the parallel and flat glass 70 insynchronization with the movement of the holding member 44 a. By makingthe area of the parallel and flat glass 70 to be larger than the movablerange of the light beams to be incident on the second fly-eye lens group40 a on a plane perpendicular to optical axis AX, the necessity of usingthe moving mechanism and the necessity of integrally securing it to theholding member 44 a can be eliminated. In this case, the necessitysimply lies in that it is mechanically secured to the apparatus.

[0172] When the light beams divided by the light dividers 20 and 21 areshifted to the concentrical direction relative to optical axis AX, it ispreferable that also the parallel and flat glass 70 is rotated relativeto optical axis AX. In a case where a plurality of the light beamsemitted from the light dividers 20 and 21 are shifted in the radialdirection and the concentrical direction relative to optical axis AX,and in particular in a case where the same are shifted in theconcentrical direction, it is preferable that the positions of thesecond fly-eye lens groups 40 a and 40 b, on which the aforesaid lightbeams are incident, are shifted so as to make coincide the direction ofthe configuration of the elements which constitute the fly-eye lensgroup and the cyclic direction of the reticle pattern to each other. Inthis case, each of the fly-eye lens groups may be made rotative or aplurality of the synthetic fly-eye lenses (the holding members 44 a and44 b) are made rotative around optical axis AX. The positions of aplurality of the light beams are shifted in the concentrical directionwhen the one-dimensional line-and-space pattern arranged regularly inthe direction X has been changed to a one-dimensional line-and-spacepattern arranged regularly in a direction inclined by 45° from the X andY directions.

[0173] A modification of the optical path difference generating memberaccording to the present invention will now be described with referenceto FIGS. 19, 20 and 21. Referring to these drawings, elements having thesame function and operation as those of the elements shown in FIG. 18are given the same reference numerals.

[0174] The modification shown in FIG. 19 is arranged in such a mannerthat the parallel and flat glass is used as the optical path differencegenerating member similarly to the aforesaid embodiment (see FIG. 18),and the parallel and flat glass 70 is disposed in a portion (an upperhalf portion above optical axis AX when viewed in the drawing) of theoptical path for the irradiation light beams which corresponds to eitherof the two inclined surfaces of the light dividers 20 and 21 (theV-shaped prism) prior to the moment the irradiation light beams from thelight source are incident on the light dividers 20 and 21. Therefore,the phase of only the light beam of the two light beams divided by thelight dividers 20 and 21, which is incident on the second fly-eye lensgroup 40 a, is delayed so that the optical path difference between thetwo light beams is made longer than coherent length LS. Referring toFIG. 19, the parallel and flat glass 70 is held by a holding member 71and the holding member 71 is held by a movable member 72 so that theparallel and flat glass 70 is able to move with respect to a stationarymember 73. The aforesaid operation is performed by an activating member74. Since the structure is arranged in such a manner that the paralleland flat glass 70 is movable in a direction perpendicular to opticalaxis AX, the parallel and flat glass 70 can be accurately disposed inthe irradiation light beam path while making optical axis AX to be theboundary. Therefore, the phase (the length of the optical path) of onlyeither of the two light beams can be changed. The portions of theapparatus shown in FIG. 19 are basically the same as those of thestructure shown in FIG. 18 and therefore their descriptions are omittedhere. In this modification, the parallel and flat glass 70 may bedisposed at any position in the optical path between a light source 80and the light dividers 20 and 21. As can be clearly seen from FIGS. 18and 19, the parallel and flat glass 70 may be disposed at any positionin the optical path between the light source 80 and the second fly-eyelens groups 40 a and 40 b. Although it may be disposed in an opticalpath between the first fly-eye lens groups 41 a and 41 b and the reticle9, it must be disposed at a position at which the light beams from thefirst fly-eye lens groups 41 a and 41 b do not superpose (for example, aposition adjacent to the emission side focal surfaces of the firstfly-eye lens groups 41 a and 41 b or a position adjacent to theirconjugated surface).

[0175]FIG. 20 illustrates a case in which a mirror is used as theoptical path difference generating member in place of the parallel andflat glass. Also this embodiment is arranged in such a manner that thelight beam portion, which corresponds to either of the two light beamsto be divided, is caused to have a phase difference (the difference inthe optical path length) prior to a moment the irradiation light beamsemitted from the light source 80 are incident on the light dividers 20and 21. Referring to FIG. 20, the irradiation light beams emitted fromthe light source 80 are divided into two light beams (the light quantityratio: 1:1) by a beam splitter (a half mirror) 70 a. The light beams,which have passed through it, then travel linearly before they areincident on the light dividers 20 and 21. On the other hand, the lightbeams reflected by the half mirror 70 a are turned upwards when viewedin the drawing before they are again turned by the reflecting mirror 70b before they are incident on the light dividers 20 and 21. As a result,the light beams reflected by the half mirror 70 a are delayed (the phaseis delayed) by the distance from the half mirror 70 a to the reflectingmirror 70 b. Therefore, also this embodiment enables the optical path ofonly either of the two light beams divided by the light dividers 20 and21 to be changed. The half mirror 70 a and the reflecting mirror 70 bare integrally secured by a holding member (omitted from illustration)while being disposed away from each other by a distance with which theoptical path difference between the two light beams is longer thancoherent length LS. Furthermore, they are disposed in the optical pathfor the irradiation light beams so as to cause the transmissive lightbeams and the reflected light beams from the half mirror 70 a to besymmetrically incident on the light divider 20 with respect to opticalaxis AX. Since this embodiment uses the mirrors 70 a and 70 b as theoptical path difference generating members, the irradiation light beamsemitted from the light source are deflected with respect to optical axisAX of the irradiation optical system as can be understood from FIG. 20.It is preferable that the structure be arranged in such a manner thatthe mirrors 70 a and 70 b are able to move in a direction perpendicularto optical axis AX so as to be able to finely adjust the incidentalpositions at which the transmitted light beams and the reflected lightbeams are incident on the light divider 20. The residual portions of theapparatus shown in FIG. 20 are the same as those of the apparatus shownin FIG. 19.

[0176]FIG. 21 illustrates an embodiment in which the structure includingthe optical path difference generating members 70 a and 70 b and thelight dividers 20 and 21 is the same as that shown in FIG. 20 but animage rotator 75 is further disposed in an optical path for one lightbeam. By virtue of the image rotator 75, only either of the light beams(the reflected light beam in the structure shown in FIG. 21) divided bythe half mirror 70 a is rotated by, for example, 180° on a planeperpendicular to optical axis AX. As a result of the aforesaidstructure, the coherence of the light beams can be further reduced andthe contrast of the speckle interference fringes acting as noisecomponents can be further lowered, causing a satisfactory advantage tobe obtained. The image rotator is not limited to the structure shown inFIG. 21 and constituted by combining prisms.

[0177] If the image rotator 75 is disposed in the optical path as inthis structure, the phase of the reflected light beams is somewhatdelayed. Therefore, it is preferable that the distance (the interval)from the half mirror 70 a and the reflecting mirror 70 b be determined.The position of the image rotator 75 is not limited to the descriptionabout this embodiment, it may be disposed at any position if it isdisposed on the optical path between the light source 80 and the reticle9 similar to the optical path difference generating member. For example,it may be disposed in the rear of the light dividers 20 and 21 (adjacentto the second fly-eye lens). Furthermore, the image rotator 75 may bedisposed more adjacent to the light source or the second fly-eye lensthan the optical path difference generating member (70 or 70 a and 70b). A similar effect can be also obtained in a case where the imagerotator 75 is disposed in the structures shown in FIGS. 18 and 19. Inother words, the conditions such as the position and the number requiredfor the image rotators 75 are the same as those required for the opticalpath difference generating member. In a case where the irradiation lightbeams emitted from the light source 80 are divided into four portions,the image rotors are disposed in the optical paths for three light beamsof the four divided light beams in such a manner that they are rotated90°, 180° and 270° respectively (the residual one is rotated by 0°) fromthe direction of the optical axis. The image rotors may be disposed inthe optical paths for the four light beams in such a manner that theyare rotated by 90°, 180°, 270° and 360° from the direction of theoptical axis.

[0178] Also the structure according to this embodiment may employ thelight divider shown in FIGS. 5 to 8. In a case where the light dividershown in FIGS. 7 and 8 is used, the optical path difference generatingmember (the parallel and flat glass 70) may be disposed in an opticalpath between the fiber emission portions 21 b and 21 c and the secondfly-eye lenses 40 a and 40 b, or in an optical path between the firstmirror 20 d and the second mirrors 21 e and 21 f (or the second fly-eyelenses 40 a and 40 b) similarly to the embodiment shown in FIG. 18, orin an optical path more adjacent to the light source than the fiberincidental portion 20 f and the first mirror 20 d similarly to theembodiment shown in FIG. 19. The number of divisions performed by eachsynthetic fly-eye lens and the light divider is not limited to two butthe divisions may be made by an arbitrary number. In the structure shownin FIG. 7, the number of divisions (the number of emission portions) ofthe fiber 20 c may be changed, while the pyramid mirror (for dividinginto four portions) may be used as the first mirror 21 d in thestructure shown in FIG. 8.

[0179] The aforesaid embodiments are formed into a two-stage integratorstructure in which the two sets of the fly-eye lenses are disposed inseries to receive a plurality of the light beams divided by the lightdividers 20 and 21. However, a square rod type optical integrator may beused as the optical integrator, or two sets of the rod type opticalintegrators are combined to each other, or the rod type opticalintegrator and the fly-eye type optical integrator may be combined toeach other to constitute the aforesaid two-stage integrator structure.An example of employment of the rod type optical integrator has beendisclosed in U.S. Pat. No. 4,952,815. As an alternative to the two-stageintegrator structure, an arrangement may be employed in which each of aplurality of light beams divided by the light dividers 20 and 21 is thendivided into a plurality of light beams by using a polyhedron prism or amirror, and a plurality of the divided light beams are caused to beincident on the incidental surface of one fly-eye lens group (a rod typeintegrator may be used) in a superposed manner.

[0180] As a result of the aforesaid structure, the illuminanceuniformity improvement effect can be somewhat obtained by using only oneoptical integrator. Furthermore, by reducing, for example, the size (thecross sectional area) of each element constituting the fly-eye lens, theilluminance uniformity can be improved to a certain degree by using onlyone mesh-type fly-eye lens. Although two sets of fly-eye lenses (40 aand 41 a) and (40 b and 41 b) are disposed to receive a plurality of thelight beams divided by the light dividers 20 and 21 in the aforesaidembodiment, either of the first fly-eye lens and the second fly-eye lensmay be formed into one large fly-eye lens which covers a region, throughwhich the light beams pass, on a plane perpendicular to optical axis AX.In this case, it is preferable that size of the fly-eye lens bedetermined while considering the movable range of the light beams on theplane perpendicular to optical axis AX corresponding to the periodicityand the precision of the reticle pattern. This fact is also adapted to acase where only one set of the fly-eye lenses is used. If the lightbeams to be incident on each fly-eye lens in the irradiation opticalsystem shown in FIGS. 18 to 21 and FIGS. 5 to 8 are used to irradiate anarea which is externally wider than the incidental end of each fly-eyelens and if the distribution of the quantity of light to be incident oneach fly-eye lens is uniform, a satisfactory effect can be obtainedbecause the illuminance uniformity on the reticle pattern surface can befurther improved.

[0181] As can be seen from the above, regardless of the structure of thelight divider and that of the fly-eye lens, a projection exposureapparatus having the irradiation optical system for forming at least twolight quantity distributions (the second light source image) on thepupil surface 17 of the irradiation optical system or on a planeadjacent to it enables the illuminance uniformity improvement effect tobe obtained on the reticle pattern surface by generating an optical pathdifference longer than coherent length LS between the light beams byusing the optical path difference generating member such as the paralleland flat glass.

[0182] In the above mentioned embodiment, the parallel and flat glass 70serving as the optical path difference generating member is disposed inthe optical path for either of the two light beams divided by the lightdividers 20 and 21. However, two parallel and flat glass members eachhaving a thickness which causes the optical path difference between thetwo light beams to be longer than coherent length LS may be disposed inthe optical paths. Furthermore, the two parallel and flat glass membersmay be integrally formed. In a case where the irradiation light beamsare divided into four portions by the light dividers 20 and 21, anoptical member 90 arranged as shown in FIG. 22A may be used which isconstituted by integrally combining parallel and flat glass plates 90 ato 90 d having different thickness. In this case, the thickness of eachparallel and flat glass is determined so as to make all of the mutualoptical path differences between the light beams which pass through theparallel and flat glass members 90 a to 90 d to be longer than coherentlength LS. It should be noted that the parallel and flat glass may beomitted from the optical path for one of the four light beams asdescribed above. As an alternative to using the parallel and flat glassas the optical path difference generating member, a stepped prism 91arranged as shown in FIG. 22B may be used. The stepped prism 91 isconstituted by, for example, combining prisms in the form of a squarerod by the same number as that of the elements which constitutes thefly-eye lens. The thickness of each prism is determined so as to makeall of the mutual optical path differences between the light beams whichpass through each prism to be longer than coherent length LS. If theaforesaid stepped prisms 91 is disposed in the optical path for onelight beam, interference generated between elements for the fly-eye lenscan be prevented and therefore the illuminance uniformity can be furtherimproved. Although the optical path difference is generated by makingthe thickness (the length) of the optical member 90 or the stepped prism91 to be different, a similar mutual optical path difference between thelight beams can be generated by constituting each of the parallel andflat glass or the prism by optical material having different refractivefactor as an alternative to employing the different thickness (lengths).

[0183] Although the aforesaid embodiment has been described about theprojection exposure apparatus having the irradiation optical system forforming at least two light quantity distributions (the secondary lightsource image of the fly-eye lens) on the pupil surface 17 of theirradiation optical system or on a plane adjacent to it, the illuminanceuniformity on the reticle pattern surface can be expected if the opticalpath difference generating member 90 shown in FIG. 22A is used in aprojection exposure apparatus which is adapted to the annular zoneirradiation method. Now, the aforesaid improvement effect will bedescribed in brief with reference to FIGS. 23A and 23B. Referring toFIG. 23A, irradiation light beam IL emitted from a light source (omittedfrom illustration) is incident on a prism 92 so as to be formed into anannular band shape, and then it is incident on a second fly-eye lens 93via the optical path difference generating member 90. The irradiationlight beams pass through a lens 94 and a first fly-eye lens 95 beforebeing used to irradiate the reticle pattern by the condenser lenses 6and 8 (see FIG. 17) with substantially uniform illuminance. Thestructures except for those shown in FIG. 23A are the same as thoseshown in FIG. 17. FIG. 23B illustrates a state where the optical pathdifference generating member 90 shown in FIG. 23A is viewed from thedirection of the optical axis. The prism 92 is a so-called cone prismhaving conical shape inclined incidental surface and the emissionsurface so that the irradiation light beams are formed into the annularband shape by the refraction effect of the prism 92 before they are usedto irradiate the optical path difference generating member 90. Both thefirst and second fly-eye lenses 93 and 95 are large fly-eye lensesextending, on a plane perpendicular to optical axis AX, to cover theregion through which the annular band shape irradiation light beamspass, the first and second fly-eye lenses 93 and 95 having elements, thecross sectional shape of each of which is very small. By employing theaforesaid structure, that is, the two-stage integrator structure and bydividing the annular band shape irradiation light beams into fourportions by the optical path difference generating member 90 and bymaking the mutual optical path difference between the divided lightbeams to be longer than coherent length LS, the illuminance uniformityon the reticle pattern surface can be improved. Although an example inwhich the annular band shape irradiation light beams are divided intofour portions is illustrated in FIG. 23, the number of divisions may bedetermined arbitrarily (however two or more). If the optical pathdifference generating member 90 is rotated relative to optical axis AXduring the exposure operation, the illuminance uniformity can be furtherimproved. In a case where the inner or the outer diameter of the annularband shape irradiation light beams is changed to correspond to theperiodicity or the precision of the reticle pattern, it is preferablethat a plurality of cone prisms having different thicknesses areexchanged by being disposed in the irradiation optical path and the size(the diameter) of the circular irradiation light beams to be incident onthe cone prism 92 can be varied by a variable aperture diaphragm.

[0184] A third embodiment of the present invention will now be describedwith reference to FIG. 24. FIG. 24 illustrates the schematic structureof this embodiment of the projection exposure apparatus. Referring toFIG. 24, the same elements as those shown in FIGS. 1 and 17 are giventhe same reference numerals. Referring to FIG. 24, the irradiation lightbeams radiated from the light source such as a mercury lamp thebrightness point of which is located at a first focal point of anelliptic mirror 2 are gathered at second focal point Al so as to besubstantially parallel beams by the input lens 4 (the collimator lens)before they are incident on a fly-eye lens 100 serving as the opticalintegrator (a plane light source forming optical system). The fly-eyelens 100 is constituted by an aggregation of a plurality of rod lenselements each having a rectangular cross section (for example, a squarecross sectional shape), the fly-eye lens 100 having emission surface A2disposed to be conjugate with a light source image formed at the secondfocal point position of the elliptic mirror 2. Therefore, a plurality oflight source images by the same number as those of the rod lens elementsconstituting the fly-eye lens 100 are formed on the emission surface A2of the fly-eye lens 10 and a secondary light source is substantiallyformed to serve as the plane light source. An aperture diaphragm 101 isdisposed in the vicinity of the position at which the secondary lightsource is formed. The light beams, which have passed through theaperture diaphragm 101, are converged by a converging lens 102 beforethey are incident on a polyhedron light source forming optical system103. The polyhedron light source forming optical system 103 (a lensarray) is composed of four lens elements (103 a, 103 b, 103 c and 103 d)disposed in parallel. Although FIG. 24 illustrates only the lenselements 103 a and 103 b, the lens elements 103 c and 103 d are disposedin parallel to the lens elements 103 a and 103 b in a directionperpendicular to the surface of the drawing sheet on which FIG. 24 isdrawn. Each of the lens elements 103 a, 103 b, 103 c and 103 d has lenssurfaces on both the incidental side and the emission side and isdisposed eccentrically so as to make the distance from its optical axisto optical axis AX of the irradiation optical system to be the same. Theaforesaid lens elements 103 a, 103 b, 103 c and 103 d are disposed tomake their emission surface A3 conjugate with the emission surface A2 ofthe fly-eye lens 100. Therefore, images (plane light source images)formed by again imaging the secondary light source are, as shown in FIG.25, formed on the emission side of the polyhedron light source formingoptical system 103 at four positions which are made to be eccentric withrespect to optical axis AX of the irradiation optical system by a numberwhich is the same as that of the lens elements. That is, four planelight sources divided by the four lens elements 103 a to 103 d areformed. As can be understood from FIGS. 24 and 25, also this embodimentemploys the inclined irradiation method similarly to the first and thesecond embodiments, and therefore a plurality of the lens elements 103 ato 103 d are disposed at the optimum positions to correspond to theprecision and the periodicity of the reticle pattern.

[0185] Referring back to FIG. 24, the four light beams formed on theemission surface A3 of each of the lens elements 103 a, 103 b, 103 c and103 d are gathered by the condenser lens 8 so as to uniformly irradiatethe reticle 9 while making a predetermined angle from optical axis AX ofthe irradiation optical system. As a result of the inclined irradiationthus performed, the light beams, which have passed through anddiffracted on the pattern of the reticle 9, are gathered and imaged bythe projection optical system 11. Hence, the image of the pattern of thereticle 9 is formed on the wafer 13.

[0186] It should be noted that the light source image A1 formed by theelliptic mirror 2, the emission surface A2 of the fly-eye lens 100 andthe emission surface A3 of the polyhedron light source forming opticalsystem 103 are disposed to be conjugated with the incidental pupilsurface 12 (an aperture diaphragm 12 a) of the projection optical systemin the irradiation optical system shown in FIG. 24. In other words, A1and A2 and A3 are Fourier transformed surfaces of the object surfaces(the reticle 9 and the wafer 13). Furthermore, the incidental surface B1of the fly-eye lens 100 and the incidental surface B2 of the polyhedronlight source forming optical system 103 are made conjugate with theobject surfaces (the reticle 9 and the wafer 13).

[0187] It is preferable that the position (the position on a planeperpendicular to the optical axis) of each lens element of thepolyhedron light source forming optical system 103 be determined inaccordance with the reticle pattern to be transferred. The method ofdetermining the position is the same as that for determining theposition of the first fly-eye lens according to the first embodiment(see FIGS. 11 and 12). That is, the position (incidental angle Φ) on thereticle on which the irradiation light beams supplied from thepolyhedron light source forming optical system 103 are incident may bedetermined so as to obtain the optimum resolution and an effect ofimproving the focal depth in accordance with the precision of thepattern to be transferred.

[0188]FIG. 26 schematically illustrates a portion from the polyhedronlight source forming optical system 103 to the projection optical system11, wherein the reticle side (rear side) focal planes 104 a and 104 b ofthe polyhedron light source forming optical system 103 coincide with theFourier transformed surface 17 of the reticle pattern 10. The condenserlens 8 for causing them to have the Fourier transformed relationship isillustrated as one lens. Furthermore, both of the distance from the lenselement side (front) principal point of the condenser lens 8 to thereticle side (rear) focal planes (104 a and 104 b) of the polyhedronlight source forming optical system 103 and the distance from thereticle side (rear) principal point of the condenser lens 8 to thereticle pattern 10 are expressed by f.

[0189] As can be understood from FIGS. 11, 12 and 26, if optical axesAxa and Axb (that is, the center of gravity of the light quantitydistribution of the secondary light source images formed by the lenselements) of each lens element of the polyhedron light source opticalsystem 103 are located on line segments Lα and Lβ, two beams passthrough positions which are distant from optical axis AX on the pupilsurface 12 of the projection optical system 11 by substantially samedistance, the two beams being composed of either of ±1-order diffractedlight beams generated from the line-and-space pattern (see FIG. 12A) dueto the irradiation of the irradiation light beams from each lens elementand 0-order diffracted light beam. That is, the focal depth with respectto the line-and-space pattern shown in FIG. 12A can be made maximum andas well as high resolution can be obtained.

[0190] Assuming that half of the distance between optical axes Axa andAxb of the corresponding lens elements 103 a and 103 b in the cyclicdirection (in the direction X) of the reticle pattern shown in FIG. 12is L (=α=β), the focal distance of the emission (rear) side of thecondenser lens 8 is f, the wavelength of the irradiation light beam is λand the pitch of the reticle pattern is P, the two lens elements 103 aand 103 b must be structured (disposed) in such a manner that thepositions of their optical axes Axa and Axb substantially satisfy anequation expressed by L=λf/2P.

[0191] In order to efficiently divide the irradiation light beams fromthe fly-eye lens 100 into two portions (to form two plane light sources)by the two lens elements 103 a and 103 b included in the polyhedronlight source forming optical system 103, it is preferable that the crosssectional shape of the lens elements in the polyhedron light sourceforming optical system 103 is formed into a rectangle and as well as thecross sectional shape of the rod lens element in the fly-eye lens 100 isformed into a rectangle similar to the overall shape of the polyhedronlight source forming optical system 103. Also the optimum positions forthe four lens elements of the polyhedron light source forming opticalsystem for use in the case of the two-dimensional pattern shown in FIG.12C are the same as those in the first embodiment (see FIG. 12D). Thatis, since the X-directional pitch of the pattern shown in FIG. 12C isPx, the optical axes of the lens elements must be located on linesegments Lα and Lβ which hold γ=ε=f·(½)·(λ/Px) as shown in FIG. 12D soas to obtain the maximum focal depth in the X-directional component ofthe pattern. Similarly, the optical axes of the lens elements must belocated on line segments Lγ and Lε which hold α=ε=f·(½)·(λ/Py) so as toobtain the maximum focal depth in the Y-directional component of thepattern.

[0192] In order to realize inclined irradiation balanced to an optimumdegree by most efficiently utilizing (most efficiently utilizing thenumber of apertures NA of the projection optical system) the size of theFourier transformed surface 17 in a case where the pitch in eachdirection of the two-dimensional pattern shown in FIG. 12 is the same(Px=Py=P), it is preferable that the structure be arranged to satisfythe relationship expressed by L=λf/2P assuming that half of the distancebetween the optical axes of each of the lens elements of the polyhedronlight source forming optical system 103 in the directions X and Y ofeach cyclic reticle pattern is L (α=β=γ=ε), the emission side (rear)focal distance of the condenser lens 8 is f, the wavelength of theirradiation light beam is λ and the pitch of the reticle pattern is P.

[0193] In this case, assuming that the number of apertures of theprojection optical system 11 facing the reticle is NAR, half of thedistance between the optical axes of each lens element of the polyhedronlight source forming optical system 103 in directions X and Y of eachcyclic reticle pattern is L (α=β=γ=ε) and the emission side (rear) focaldistance of the condenser lens 8 is f, the structure may be arranged tomeet the following relationship:

0.35NAR≦L/f≦0.7 NAR

[0194] If the relationship becomes smaller than the lower limit of thisequation, the effect obtainable by virtue of the inclined irradiationdeteriorates and therefore high resolution cannot be realized whilemaintaining a large focal depth even if the inclined irradiation isperformed. If the same exceeds the upper limit of the aforesaidequation, a problem arises in that the light beams supplied from aseparated light source formed on the Fourier transformed surface cannotass through the projection optical system.

[0195] A fourth embodiment of the present invention will now bedescribed with reference to FIG. 27. FIG. 27 is a view which illustratesthe schematic structure of this embodiment of the projection exposureapparatus, wherein the elements having the same functions as those ofthe elements of the third embodiment shown in FIG. 24 are given the samereference numerals. The difference from the third embodiment lies in afact that an optical function equivalent to the fly-eye lens 100 isrealized by using a converging lens 105, a rod type optical integrator106 and a converging lens 107.

[0196] In the structure according to this embodiment, the light sourceimage converged at the second focal point A1 by the elliptic mirror 2 isrelayed to the incidental surface A2 of a square rod type opticalintegrator 106 by the input lens 4 and the converging lens 105. Thelight beams emitted from the incidental surface A11 of the rod typeoptical integrator 106 are reflected by the inner surface of the rodtype optical integrator 106 and then they are emitted from the emissionsurface B11. At this time, the light beams emitted from the emissionsurface B11 are substantially emitted as if there are a plurality oflight source images (plane light surface) at the incidental surface A11of the rod type optical integrator 106. As for details of this, refer toU.S. Pat. No. 4,952,815.

[0197] The light beams emitted from the rod type optical integrator 106are converged by the converging lens 107 so that a plurality of lightsource images are formed at the emission side (rear) focal point A2.Hence, a substantially secondary plane light source is formed. Since theaperture diaphragm 101 is disposed at the secondary light sourceposition, the light beams, which have passed through it, are convergedby a converging lens 108. Then, four third plane light sources separatedby the polyhedron light source forming optical system 103 are formed sothat the reticle 9 is inclined-irradiated in the superposed manner viathe condenser lens 8. As a result of the structure thus arranged, highresolution can be realized while maintaining a large focal depthsimilarly to the third embodiment.

[0198] It should be noted that the light source image A1 formed by theelliptic mirror 2, the incidental surface A11 of the rod type opticalintegrator 106, the emission side (rear) focal point position A2 of theconverging lens 107 and the emission surface A3 of the polyhedron lightsource forming optical system 103 are disposed to hold the conjugaterelationship with the incidental pupil 12 (the aperture diaphragm 12 a)of the projection optical system 12. In other words, A1, A11, A2 and A3are Fourier transformed surfaces of the object surfaces (the reticle 9and the wafer 13). Furthermore, the emission surface B11 of the rod typeoptical integrator 106 and the incidental surface B2 of the polyhedronlight source forming optical system 103 are relayed by the converginglenses 107 and 108 so that they are disposed in conjugation with theobject surface (the reticle 9 and the wafer 13).

[0199] As an alternative to the rod type optical integrator constitutedby square rod optical members, a hollow and square rod reflectingoptical member constituted by forming a reflecting member into a squarerod shape may be used. Furthermore, the cross sectional shape of the rodtype optical integrator is not limited to the rectangular. It may, ofcourse, be formed into a polygonal or cylindrical shape.

[0200] The third embodiment shown in FIG. 24 is arranged in such amanner that the variable aperture diaphragm 101 the caliper of which canbe varied is formed adjacent to the emission surface of the fly-eye lens100, while the fourth embodiment shown in FIG. 27 is arranged in such amanner that the variable aperture diaphragm 101 is disposed at theemission side (rear) focal point position of the converging lens 107.The variable aperture diaphragm 101 is able to vary the size of thelight source image to be formed on the emission surface of thepolyhedron light source forming optical system 103 by varying itscaliper. Therefore, by controlling the size of the light source image tobe formed on the pupil surface of the projection optical system, theinclined irradiation can be performed with a proper a value. That is, itis preferable that the size of the light source image formed by eachlens element included by the polyhedron light source forming opticalsystem 103 be made in such a manner that the number of apertures (thesingle width of the angular distribution on the reticle) per emittedlight beam with respect to the number of apertures of the projectionoptical system facing the reticle is about 0.1 to 0.3. If it is smallerthan 0.1 times, the accuracy of the transferred pattern (image)deteriorates. If the same is 0.3 times or more, the effect of obtaininghigh resolution and a large focal depth become unsatisfactory.

[0201] The variable aperture diaphragm for varying the value σ may bedisposed adjacent to the emission side of the polyhedron light sourceforming optical system 103. In this case, it is preferable that avariable aperture diaphragm is used which has variable apertures by thenumber which is the same as that of the lens elements which constitutethe polyhedron light source forming optical system 103. Furthermore, forexample, a so-called turret system in which a plurality of apertureshaving different calipers are formed in a disc in place of the variableaperture diaphragm and it is rotated as desired may be employed to varythe size of the light source image for the purpose of obtaining anoptimum value σ.

[0202] In order to vary the value a while preventing the shieldingoperation performed by the aperture diaphragm, an afocalmagnification-varying optical system 110 may be disposed in an opticalpath between the input lens 4 and the fly-eye lens 100 and the secondarylight source image to be formed by the emission surface A2 of thefly-eye lens 100 may be efficiently varied by the operation of varyingthe magnification performed by the afocal magnification-varying opticalsystem 110.

[0203]FIG. 28 illustrates the optical structure more adjacent to thelight source than the fly-eye lens 100 shown in FIG. 25, wherein theafocal magnification-varying optical system 110 is composed of apositive first lens group 110 a, a negative second lens group 110 b anda positive first lens group 110 c. As shown in FIGS. 28A and 28B, themagnification can be varied by moving each of the lens groups 110 a to110 c so that the size of the secondary light source formed on theemission side of the fly-eye lens can be varied while preventing thefact that the light beams are shielded.

[0204] Also by virtue of the magnification variation performed by theafocal magnification-varying optical system 110, the incidental surface(B1) of the fly-eye lens is made substantially conjugate with aperture 2a (B2 a) of the elliptic mirror with respect to the input lens 4 and theafocal magnification-varying optical system 110. As a result, the valuea can be efficiently varied while maintaining the double conjugatedrelationship with the object surface and the pupil surface (Fouriertransformed surface).

[0205] In this case, an arrangement may be employed in which informationsuch as the width of the lines of the reticle is supplied to input meansand the drive system for varying the diameter of the aperture of theaperture diaphragm is driven in accordance with calculated informationso as to automatically obtain the optimum value σ. Furthermore, astructure may be employed in which a bar code or the like havinginformation about the line width of the reticle pattern is fastened tothe reticle, detection means for detecting information is provided andthe drive system for varying the caliper of the aperture diaphragm isdriven in accordance with detected information so as to set an optimumvalue σ.

[0206] Although the embodiments shown in FIGS. 24 and 27 are arranged insuch a manner that the light beams from a source such as the mercurylamp are converged by the elliptic mirror and they are made intoparallel beams by the input lens 4, another structure may be employed inwhich a light source such as an excimer laser for supplying parallelbeams is used and the parallel beams from the laser beam source arecaused to be incident on, in the structure shown in FIG. 24, the fly-eyelens 100, or, in the structure shown in FIG. 27, on the converging lens105. In particular, in the third embodiment shown in FIG. 24, the shapeof the emission surface A2 of the fly-eye lens 100 may be formed into aplane because the secondary light source image formed on the emissionsurface A2 of the fly-eye lens 110 is a spot light source havingsubstantially no area. Furthermore, in a case where a light source suchas the excimer laser capable of emitting large output is used, lightenergy is concentrated on the emission surface A2 of the fly-eye lens100 and the emission surface A3 of each lens element of the polyhedronlight source forming optical system 103. Therefore, it is preferablethat the focal point positions of the incidental surfaces B1 and B2 belocated in a space outer than the corresponding emission surfaces A1 andA3 in order to maintain the durability of the fly-eye lens 100 and thepolyhedron light source forming optical system 103.

[0207] Furthermore, in order to realize the optimum inclined irradiationfor each cyclic line width of the reticle pattern under a highirradiation efficiency, it is preferable that the structure be arrangedin such a manner that an exchange is enabled for another polyhedronlight source forming optical system composed of four lens elementshaving different size and the positions of optical axes with respect tothe optical axis of the irradiation optical system form the four lenselements which constitute the polyhedron light source forming opticalsystem. Furthermore, it is preferable to employ a structure to changethe reticle side number of apertures NA of the plane light sourceforming optical system (the fly-eye lens) for forming the plane lightsource more adjacent to the light source than the polyhedron lightsource forming optical system, the NA of the rod type optical integrator106 and that of the converging lens 107.

[0208] As a preferred structure for changing the reticle side number ofapertures NA of the plane light source forming optical system, it ispreferable to employ a zoom lens type fly-eye lens in the structureshown in FIG. 24 or to arrange the structure in such a manner thatexchange can be enabled for another focal distance. It is preferable toarrange the structure in such a manner that exchange is enabled foranother rod type optical integrator having a different thickness andlength from those of the rod type optical integrator 106 in thestructure shown in FIG. 27. In particular, it is preferable to move theconverging lens 105 in the direction of the optical axis by a distancecorresponding to the change in the length of the rod type opticalintegrator when the rod type optical integrator is exchanged.

[0209] Furthermore, the illuminance uniformity of a plurality of theplane light sources to be formed by the polyhedron light source formingoptical system 103 may be further improved by disposing another planelight source forming optical system more adjacent to the light sourcethan the polyhedron light source forming optical system 103 in theirradiation optical system according to each embodiment.

[0210] A fifth embodiment of the present invention will now be describedwith reference to FIG. 29. FIG. 29 is a view which illustrates theschematic structure of this embodiment of the projection exposureapparatus. Referring to FIG. 29, the same elements as those shown inFIG. 1 are given the same reference numerals. Referring to FIG. 29, theirradiation light beams radiated from the light source such as a mercurylamp are converged by the elliptic mirror 2, and then they are made intosubstantially parallel beams by the input lens (collimator lens) 4before they are incident on the light dividing optical systems 200 and201. The light dividing optical systems are composed of the firstpolyhedron prism 200 having a V-shaped concave and the polyhedron prism201 having a V-shaped convex. As a result of the refraction effect ofthe two prisms, the irradiation light beams are divided into two beams.Each light beam is incident on an Individual first plane light sourceforming optical system composed of elements 202 a, 203 a and 204 a and asecond plane light source forming optical system composed of elements202 b, 203 b and 204 b.

[0211] Although the two plane light source forming optical systems areused, the number of them may be determined arbitrarily. Furthermore,although the light dividing optical system is divided into two sectionsto correspond to the number of the plane light source forming opticalsystems, the number of divisions may be arbitrary determined tocorrespond to the number of the polyhedron light source forming opticalsystem. For example, the light dividing optical systems 200 and 201 mayrespectively be composed of a first polyhedron prism (see FIG. 30A)having a pyramid concave and a second polyhedron prism (see FIG. 30B)having a pyramid convex.

[0212] Each plane light source forming optical system is composed offirst converging lenses 202 a and 202 b, rod type optical integrators203 a and 203 b and second converging lenses 204 a and 204 b. The lightbeams divided into two portions by the light dividing optical systems200 and 201 are converged by the first converging lenses 202 a and 202 bbefore they are incident on the rod type optical integrators 203 a and203 b. Each of the rod type optical integrators 203 a and 203 b isconstituted by a square rod type optical member having the incidentalsurface A2 located at the converging point of the first converginglenses 202 a and 202 b or at a position adjacent to it, the incidentalsurface A2 being disposed substantially conjugate with the light sourceimage position A1 of the image formed by the elliptic mirror 2. Thelight beams, which have been incident on the rod type opticalintegrators 203 a and 203 b are reflected by their inner surfaces beforethey are emitted from the emission surface B1. Hence, the emitted lightbeams from the emission surface B1 emit as if there are a plurality oflight source images (plane light sources) on the incidental surface A2.The aforesaid function has been disclosed in U.S. Pat. No. 4,952,815 indetail.

[0213] The irradiation light beams emitted from the rod type opticalintegrators 203 a and 203 b are converged by the second converginglenses 204 a and 204 b so that two secondary light sources are formed atthe emission side (rear) focal point position A3 of the aforesaid lenssystem. Therefore, substantially two plane light sources are formed. Theaperture diaphragm 205 having two apertures is disposed at the positionA3 at which the secondary light sources are formed so that each lightbeam, which has passed through each aperture of the aperture diaphragm205 is converged by the condenser lens 8. As a result, the reticle 9 isinclined-irradiated at a predetermined inclination.

[0214] A predetermined circuit pattern is formed on the lower surface ofthe reticle 9 and the light beams, which have passed through and havebeen diffracted by the reticle pattern, are converged and imaged by theprojection optical system 11. As a result, the pattern of the reticle 9is formed on the wafer 13.

[0215] In the irradiation optical system shown in FIG. 29, the lightsource image Al formed by the elliptic mirror 2, the incidental surfacesA2 of the rod type optical integrators 203 a and 203 b, and the emissionside (rear) focal point positions A3 of the second converging lenses 204a and 204 b are conjugate with the incidental pupil surface 12 (theaperture diaphragm 12 a) of the projection optical system 11. In otherwords, A1, A2 and A3 are Fourier transformed surfaces of the objectsurfaces (the reticle 9 and the wafer 13). Furthermore, the emissionsurfaces B1 of the rod type optical integrators 203 a and 203 b areconjugate with the object surfaces (the reticle 9 and the wafer 13).

[0216] As described above, the first plane light source forming opticalsystem composed of the elements 202 a, 203 a and 204 a and the secondplane light source forming optical systems composed of the elements 202b, 203 b and 204 b are located away from optical axis AX. Therefore, thefocal depth of a pattern of the patterns of the reticle 9 having aspecific direction and a pitch can be considerably enlarged.

[0217]FIG. 31 is an enlarged view which illustrates a portion from thelight dividing optical systems 200 and 201 to the second converginglenses 204 a and 204 b shown in FIG. 29. Assumptions are made here thatthe facing surface of the first polyhedron prism 200 and the secondpolyhedron prism 201 are parallel to each other and the incidentalsurface of the prism 200 and the emission surface of the prism 201 areperpendicular to optical axis AX. Referring to FIG. 31, the sameelements as those shown in FIG. 2 are given the same reference numeralsand their descriptions are omitted here. The first polyhedron prism 200is held by the holding member 23.

[0218] A plurality of light beams emitted from the polyhedron prism 201are incident on the first converging lenses 202 a and 202 b. Referringto FIG. 31, the first plane light source forming optical system composedof the elements 202 a, 203 a and 204 a is held by the holding member 44a, while the second plane light source forming optical system composedof the elements 202 b, 203 b and 204 b is held by the holding member 44b.

[0219] By integrally holding and moving the first plane light sourceforming optical system composed of the elements 202 a, 203 a and 204 aand the second plane light source forming optical system composed of theelements 202 b, 203 b and 204 b, the position of the light beams emittedfrom the second converging lenses 204 a and 204 b can be arbitrarilyshifted on a plane perpendicular to optical axis AX.

[0220] Although the structure shown in FIG. 31 is arranged in such amanner that the position of each divided light beam can be radiallyshifted with respect to optical axis AX by changing the interval betweenthe light dividing optical systems (the polyhedron prisms) 200 and 201in the optical axial direction, each light beam may be shifted in theconcentrical direction relative to optical axis AX.

[0221] Also in this embodiment similarly to the aforesaid embodiments,it is preferable that the positions (the positions on the planeperpendicular to the optical axis) of the first plane light sourceforming optical system composed of the elements 202 a, 203 a and 204 aand the second plane light source forming optical system composed of theelements 202 b, 203 b and 204 b be determined (changed) in accordancewith the reticle pattern to be transferred. It is preferable in thiscase that the method of determining the positions be arranged asdescribed above in such a manner that the positions (incidental angle φ)on which the irradiation light beams form each plane light sourceforming optical system are incident on the reticle pattern aredetermined so as to realize the optimum resolution and obtain the effectof improving the focal depth with respect to the precision of thepattern to be transferred. The description about the optimumconfiguration of the plane light source forming optical systems isomitted here. As a result of the aforesaid structure, also thisembodiment enables the focal depth to be made largest with respect tothe reticle pattern while realizing high resolution.

[0222] A sixth embodiment of the present invention will now be describedwith reference to FIG. 32. FIG. 32 is a view which illustrates theschematic structure of the projection exposure apparatus according tothis embodiment. Referring to FIG. 32, the same elements as those of thefifth embodiment (see FIG. 29) are given the same reference numerals.The difference from the fifth embodiment lies in that fly-eye lenses 300a and 300 b are disposed in plane of the first converging lenses 202 aand 202 b.

[0223] Referring to FIG. 32, the irradiation light beams radiated fromthe light source 1 such as a mercury lamp are converged by the ellipticmirror 2 and then they are made to be substantially parallel beams bythe input lens (the collimator lens) 4 before they are divided by thelight dividing optical systems 200 and 201. The two divided parallelbeams are incident on the fly-eye lenses 300 a and 300 b made ofaggregates of rod lens elements having a rectangular cross section (forexample, a square cross section) so as to be converged on their emissionsurfaces A2 or portions adjacent to the emission surfaces A2. As aresult, a plurality of spot light sources are formed. The plane lightsource substantially serving as the secondary light source is formed inthe aforesaid position. The incidental surfaces of the rod type opticalintegrators 203 a and 203 b are located adjacent to the emissionsurfaces of the fly-eye lenses 300 a and 300 b. Therefore, theincidental surfaces of the rod type optical integrators 203 a and 203 bare disposed substantially conjugate with the light source imageposition A1 of the image formed by the elliptic mirror 2. The rod typeoptical integrators 203 a and 203 b are made of rectangular rod shapeoptical members so that the incidental light beams are reflected bytheir inner surfaces and emitted from the emission surface B1 asdescribed above. Hence, the light beams are emitted from the emissionsurface B1 as if there are a plurality of the light source images (theplane light source) on the aforesaid incidental surface A2.

[0224] The irradiation light beams emitted from the rod type opticalintegrators 203 a and 203 b are converged by the converging lenses 204 aand 204 b so that two plane light source images serving as the thirdlight sources are formed at eccentric positions from optical axis AX atthe emission side focal point position of the lens. Therefore, theilluminance distribution of the light beams on the emission surfaces ofthe fly-eye lenses 300 a and 300 b are made uniform by the integrationeffect. Furthermore, the light beam illumination distribution at theemission side focal point position A3 of the converging lenses 204 a and204 b can be further satisfactorily made uniform by the rod type opticalintegrators 203 a and 203 b.

[0225] The aperture diaphragm 205 having two apertures is disposed atthe position A3 at which the two plane light sources serving as thethird light sources are formed. Each light beam which has passed throughthe aperture diaphragm 205 is converged by the condenser lens 8 so thatit is used to uniformly irradiate the reticle 9 at a predeterminedangle. The light beams which have passed through and been diffracted bythe reticle pattern in the inclined irradiation manner are converged andimaged by the projection optical system 11, so that the image of thepattern of the reticle 9 is formed on the wafer 13.

[0226] As described above, the first plane light source forming opticalsystem composed of elements 300 a, 203 a and 204 a and the second planelight source forming optical system composed of elements 300 b, 203 band 204 b are disposed away from optical axis AX. Therefore, the focaldepth of the projected image of the pattern of the patterns of thereticle having a specific direction and pitch can be considerablyenlarged.

[0227] In the irradiation optical system shown in FIG. 32, the lightsource image A1 formed by the elliptic mirror 2, the emission surfaces(the incidental surfaces of the rod type optical integrators 203 a and203 b) A2 of the fly-eye lenses 300 a and 300 b and the emission sidefocal point positions A3 of the second converging lenses 204 a and 204 bare conjugate with the incidental pupil 12 (the aperture diaphragm 12 a)of the projection optical system 11. In other words, A1, A2 and A3 areFourier transformed surfaces of the object surfaces (the reticle 9 andthe wafer 13). Furthermore, the incidental surfaces B11 of the fly-eyelenses 300 a and 300 b and the emission surfaces B1 of the rod typeoptical integrators 203 a and 203 b are conjugate with the objectsurfaces (the reticle 9 and the wafer 13).

[0228] Although the sixth embodiment shown in FIG. 32 is arranged insuch a manner that the light beams are divided into two portions by thelight dividing optical systems 200 and 201, another structure may beemployed in which the prism shown in FIG. 30 is used and four planelight source forming optical systems are disposed in parallel tocorrespond to the prism facing the reticle so as to form four planelight sources on the Fourier transformed surface.

[0229] A seventh embodiment of the present invention will now bedescribed with reference to FIG. 33. Referring to FIG. 33, the sameelements as those of the fifth embodiment shown in FIG. 29 are given thesame reference numerals. The difference from the fifth embodiment liesin that the function equivalent to that realized by the first planelight source forming optical systems composed of the elements 300 a, 203a and 204 a and the second plane light source forming optical systemcomposed of the elements 300 b, 203 b and 204 b is realized by oneoptical system composed of the first converging lens 210, the rod typeoptical integrator 211 and the second converging lens 212.

[0230] Referring to FIG. 33, the irradiation light beams radiated fromthe light source 1 such as a mercury lamp are converged by the ellipticmirror 2 and then they are made to be substantially parallel beams bythe input lens (the collimator lens) 4 before they are divided into twoportions by the light dividing optical systems 200 and 201. The twodivided parallel beams are converged to the emission side (rear) focalpoint position by the first converging lens 210. The incidental surfacesof the rod type optical integrator 211 is located at the focal pointposition A2, the incidental surfaces being substantially conjugate withthe light source image position A1 of the image formed by the ellipticmirror 2.

[0231] As described above, the light beams which have been incident onthe rod type optical integrator 211 are reflected by the inner surfaceof it before they are emitted from the emission surface B1. Therefore,the light beams are emitted from the emission surface B1 as if there area plurality of the light source images (the plane light sources) on theincidental surface A2. Then, the light beams are converged by the secondconverging lens 212 so that two plane light source images separated fromeach other and serving as the secondary light sources are formed at theemission side (rear) focal point position A3 of the lens 212. The reasonfor this lies in a fact that the light beams are incident on the rodtype optical integrator in a state where they are separated from eachother while making the same angle.

[0232] The aperture diaphragm 205 having two apertures is disposed atthe position A3 at which the two plane light source images serving asthe second light source are formed. The light beams which have passedthrough the aperture diaphragm 205 are converged by the condenser lens 8so that the reticle 9 is uniformly irradiated with them while beinginclined at a predetermined angle. A predetermined circuit pattern isformed on the lower surface of the reticle 9 so that the light beamswhich have passed through and been diffracted by the reticle pattern bythe inclined irradiation method are converged and imaged by theprojection optical system 11. Hence, the image of the pattern of thereticle 9 is formed on the wafer 13.

[0233] As described above, the positions of the centers of gravity ofthe two plane light sources (the secondary light sources) formed by thepolyhedron light source forming optical systems 210, 211 and 212 arelocated distant from optical axis AX. Therefore, the focal depth of theprojected image of the pattern of the patterns of the reticle 9 having aspecific direction and pitch can be considerably enlarged.

[0234] According to this embodiment, by only changing the air intervalbetween the two polyhedron prisms which constitute the light dividingoptical systems 200 and 201, the incidental angle of the divided lightbeams to be incident on the incidental surface A2 of the rod typeoptical integrator can be varied. Hence, the position of the secondarylight source image to be formed on the emission side (rear) focal pointposition A3 of the second converging lens 212 with respect to opticalaxis AX of the secondary light source image can be controlled.

[0235] In the irradiation optical system shown in FIG. 33, the lightsource image Al formed by the elliptic mirror 2, the incidental surfaceA2 of the rod type optical integrator 211 and the emission side focalpoint position A3 of the second converging lens 212 are conjugate withthe incidental pupil 12 (the aperture diaphragm 12 a) of the opticalprojection system 11. In other words, A1, A2 and A3 are Fouriertransformed plane of the object surface (the reticle 9 and the wafer13). Furthermore, the emission surface B1 of the rod type opticalintegrator 211 is conjugate with the object surface (the reticle 9 andthe wafer 13).

[0236] Although the seventh embodiment shown in FIG. 33 is arranged insuch a manner that the light beams are divided into two portions by thelight dividing optical systems 200 and 201, another structure may beemployed in which the prism shown in FIG. 30 is used to form four planelight sources on the Fourier transformed surface.

[0237] In the embodiments shown in FIGS. 29, 32 and 33, the variableaperture diaphragms 205 disposed at the two or three dimensional planelight source position formed by each polyhedron light source formingoptical system are able to vary the size of the light source image byvarying the caliper of the variable aperture diaphragm 205. Therefore,by controlling the size of the light source image to be formed on thepupil surface of the projection optical system 11, the optimum inclinedirradiation with a proper value σ can be performed.

[0238] As for the size of the plane light source image to be formed byeach polyhedron light source forming optical system, it is preferablethat the number of apertures (a single width of the angle distributionon the reticle) per one emitted light beam be about 0.1 to about 0.3with respect to the reticle side number of apertures of the projectionoptical system. If it is smaller than 0.1 times, the correctivity of thepattern transference deteriorates. If it is larger than 0.3 times, aneffect of improving the resolution and that of realizing a large focaldepth cannot be obtained.

[0239] As an alternative to the variable aperture diaphragm, a so-calledturret system may be employed in which a disc having a plurality ofapertures having different calipers is used so as to be rotated asdesired for the purpose of obtaining the optimum value a by changing thesize of the light source image.

[0240] In the embodiments shown in FIGS. 29, 32 and 33, the structure isarranged in such a manner that the light beams form the light source 1such as a mercury lamp are converged by the elliptic mirror 2 so as tomake them the parallel beams by the input lens 4. As an alternative tothis, an epoxy laser or the like for supplying parallel beams may beemployed as the light source to cause the parallel light beams from thelaser beam source to be incident on the light dividing optical systems200 and 201. In particular, in the sixth embodiment shown in FIG. 32,spot light sources having substantially no size are formed as the lightsource image to be formed on the emission surfaces A2 of the fly-eyelenses 300 a and 300 b and therefore the shape of the emission surfacesA2 of the fly-eye lenses 300 a and 300 b may be formed into a flatshape. In a case where a large output light source such as the excimerlaser is used, optical energy is concentrated on the emission surfacesA2 of the fly-eye lenses 300 a and 300 b. Hence, it is preferable thatthe focal points of the incidental surfaces B1 of the fly-eye lenses 300a and 300 b are located in a space outside the emission surface A1 inorder to maintain the durability of the fly-eye lenses 300 a and 300 b.

[0241] Although the invention has been described in its preferred formwith a certain degree of particularly, it is understood that the presentdisclosure of the preferred form may be changed in the details ofconstruction and the combination and arrangement of parts withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

1. An exposure apparatus which exposes an object with an illuminationbeam irradiated on a mask from a light source, comprising: anillumination optical system disposed on an optical path along which theillumination beam passes to illuminate the mask with the illuminationbeam through an optical integrator; an optical unit disposed between thelight source and the optical integrator in the illumination opticalsystem to form different intensity distributions of the illuminationbeam on a Fourier transform plane with respect to a pattern surface ofthe mask, one of the different intensity distributions having anincreased intensity portion apart from an optical axis of theillumination optical system relative to a portion of the one intensitydistribution on the optical axis, and the optical unit including a firstelement to adjust a position of the increased intensity portion in afirst direction on the Fourier transform plane and a second element toadjust the position of the increased intensity portion in a seconddirection perpendicular to the first direction.
 2. An apparatusaccording to claim 1, wherein said one intensity distribution has aplurality of increased intensity portions of which distances from saidoptical axis are substantially equal.
 3. An apparatus according to claim2, wherein said optical unit includes a zoom optical system to change asize of said illumination beam.
 4. An apparatus according to claim 3,wherein said first and second elements are moved along said optical axisrespectively to adjust positions of said plurality of increasedintensity portions.
 5. An exposure apparatus which exposes an objectwith an illumination beam irradiated on a mask from a light source,comprising: an illumination optical system disposed on an optical pathalong which the illumination beam passes to illuminate the mask with theillumination beam through an optical integrator; an optical unitdisposed between the light source and the optical integrator in theillumination optical system to form different intensity distributions ofthe illumination beam on a Fourier transform plane with respect to apattern surface of the mask, first one of the different intensitydistributions having an increased intensity portion apart from anoptical axis of the illumination optical system relative to a portionapart from an optical axis of the illumination optical system relativeto a portion of the first intensity distribution on the optical axis,and the optical unit including a first optical element that deflects theillumination beam from the optical axis to form the first intensitydistribution, a second optical element exchanged for the first opticalelement to form second one of the different intensity distributions andan optical device to change a size of said illumination beam on theFourier transform plane.
 6. An apparatus according to claim 5, whereinsaid optical device includes a zoom optical system.